Tuberculosis: An Overview
Wanda Cruz-Knight, MD, MBA*, Lyla Blake-Gumbs, MD, MPH
Department of Family Medicine and Community Health, University Hospitals Case Medical
Center, Case Western Reserve University School of Medicine, 11100 Euclid Avenue, Cleveland,
OH 44118, USA
* Corresponding author.
E-mail address: Wanda.Cruz-Knight@UHhospitals.org
KEYWORDS
Latent tuberculosis infection Clinical presentations tuberculosis
Treatment of tuberculosis Genital tuberculosis Transmission of tuberculosis
KEY POINTS
Tuberculosis (TB) is still a public health issue. TB continues to reign as one of the world’s
deadliest diseases. One-third of the world’s population has been infected with TB. Identified cases of mycobacterium must be notified in an attempt to reduce the public health
impact of TB on the population.
The principal cause of tissue destruction from Mycobacterium tuberculosis (MTB) infection is related to an organism’s ability to incite intense host immune reactions to antigenic
cell wall proteins.
TB transmission occurs via inhalation of droplet nuclei. Person-to-person transmission
continues to present significant public health issues as work continues toward decreasing
the spread of TB.
The Centers for Disease Control and Prevention (CDC) recommends that high-risk populations in the United States be screened for latent infection, including HIV patients, intravenous (IV) drug users, health care workers who serve high-risk populations, and contacts
of individuals with pulmonary TB.
The most common site for the development of TB is the lungs; 85% of patients with TB
present with pulmonary complaints. Extrapulmonary TB may present with primary infection or can be accompanied by reactivation.
Tuberculin skin test (TST) and interferon-g release assay (IGRA) are the standard methods
for identifying persons infected with the mycobacterium.
TB may clinically manifest as primary TB, reactivation TB, laryngeal TB, endobronchial TB,
lower lung field TB infection, and tuberculoma. Clinical manifestations of TB vary according to site of mycobacterial proliferation.
Primary pulmonary TB is often accompanied by a normal chest radiograph. Hilar adenopathy is the most common chest abnormality.
Treatment of TB depends on whether latent TB infection (LTBI) or active TB is treated.
Initial empiric treatment of MTB consists of a 4-drug regimen: isoniazid, rifampin, pyrazinamide, and either ethambutol or streptomycin. Once the MTB isolate is known to be fully
susceptible, ethambutol (or streptomycin, if it is used as a fourth drug) can be discontinued. Patients diagnosed with active MTB should undergo sputum analysis for MTB weekly
until sputum conversion is documented. Treatment duration is typically 6 to 9 months.
Prim Care Clin Office Pract 40 (2013) 743–756
http://dx.doi.org/10.1016/j.pop.2013.06.003 primarycare.theclinics.com
0095-4543/13/$ – see front matter 2013 Elsevier Inc. All rights reserved.
INTRODUCTION
TB is an infectious disease caused by MTB. Mycobacterium commonly affects the
lungs but may affect almost any organ system, including the lymph nodes, central nervous system, liver, bones, genitourinary tract, and gastrointestinal tract. TB is highly
transmissible through respiratory droplets. Identified cases of mycobacterium must
be notified in an attempt to reduce the public health impact of TB on the population.
MYCOBACTERIUM TUBERCULOSIS
MBT is large nonmotile rod-shaped obligate aerobic bacterium requiring oxygen for
survival. Commonly introduced to the body through inhalation of droplet nuclei,
MTB is usually found in well-aerated upper lobes of the longs.1 As a facultative intracellular parasite, the bacterium inhabits macrophages, multiplying within the macrophages. As the bacterium proliferates, they are released from dying macrophages
into the alveolar environment. The fate of the mycobacterium is dependent on the
host’s immune system. A healthy immune system may clear the bacterium whereas
exposure may also lead to LTBI or progress to primary TB.
The cellular immune system leads to successful containment of TB. This response is
mediated by helper T cells. The ability of T cells and macrophages to block the proliferating bacterium, by forming a granuloma consisting of a caseous center (necrotic
cells) surrounded by macrophages and lymphocytes, prevents the growth and spread
of mycobacterium. This is the basis for LTBI, where a person infected with MTB does
not currently have active TB disease.2 Unfortunately, 5% to 10% of persons with LTBI
are at risk of progressing to active TB; therefore, the authors most actively identify individuals with LTBI and treat to prevent progression to active TB. Individuals with LTBI
are noninfectious. Immunocompromised individuals, such as those with HIV infection,
cancer, or patients on immunosuppressing medications, are at higher risk of progression to active TB from primary infection or reactivation.
PATHOPHYSIOLOGY
Transmission occurs when inhaled droplet nuclei are deposited within the terminal airspaces of the lung. A cellular immune response that can be detected by a reaction to
the TST occurs when tuberculi numbers reach 1000 to 10,000. This usually occurs
within 2 to 12 weeks after infection.3
MTB have multiple cell wall constituents consisting of glycoproteins, phopholipids,
and wax D.1 These constituents activate Langerhans cells, lymphocytes, and polymorphonuclear leukocytes. Their antigenicity promotes a vigorous, nonspecific immune response. Infection MTB does not always lead to actual TB. The infection
may be cleared by the host immune system or suppressed into an inactive form,
LTBI, with resistant hosts controlling mycobacterial growth at distant foci before the
development of disease. Patients with LTBI cannot spread TB.
The most common site for the development of TB is the lungs; 85% of patients with
TB present with pulmonary complaints. Extrapulmonary TB may present with primary
infection or can be accompanied by reactivation.
Common extrapulmonary sites are as follows:
Mediastinal, retroperitoneal, and cervical (scrofula) lymph nodes—the most common site of tuberculous lymphadenitis (scrofula) is in the neck, along the sternocleidomastoid muscle; it is usually unilateral and causes little or no pain;
advanced cases of tuberculous lymphadenitis may suppurate and form a draining sinus
744 Cruz-Knight & Blake-Gumbs
Vertebral bodies
Adrenals
Meninges
Gastrointestinal tract
The principal cause of tissue destruction from MTB infection is related to an organism’s ability to incite intense host immune reactions to antigenic cell wall proteins.
Mycoplasm forms spherical tubercles consisting of up to 3-mm nodules with approximately 4 cellular zones. The lesions are epithelioid granulomas with central caseation
necrosis. The primary lesion is usually found within alveolar macrophages in subpleural regions of the lung; local proliferation of bacilli occurs and spread through the lymphatics to a hilar node, forming the Ghon complex.
Tuberculi nodules consist of
A central caseation necrosis
An inner cellular zone of epithelioid macrophages and Langerhans giant cells admixed with lymphocytes
An outer cellular zone of lymphocytes, plasma cells, and immature macrophages
A rim of fibrosis (in healing lesions)
Healing of tuberculin lesions may take various forms and stages. Initial lesions may
heal and the infection become latent before symptomatic disease occurs. Smaller tubercles may resolve completely. Fibrosis occurs when hydrolytic enzymes dissolve tubercles and larger lesions are surrounded by a fibrous capsule. Such fibrocaseous
nodules usually contain viable mycobacteria and are potential lifelong foci for reactivation or cavitation. Some nodules calcify or ossify and are seen easily on chest
radiographs.
Tissues within areas of caseation necrosis have high levels of fatty acids, low pH,
and low oxygen tension, all of which inhibit growth of the tubercle bacillus.1 The body’s
immune responses ability to manage this initial infection and the proliferation of mycoplasm prevent development of primary TB. Otherwise, purulent exudates with large
numbers of acid-fast bacilli (AFB) become present in sputum and tissue. Subserosal
granulomas may rupture into the pleural or pericardial spaces and create serous
inflammation and effusions. The immune systems response to the mycobacteria
may lead to either proliferative or exudative lesions. Both types of lesions can develop
in the same host, because infective dose and local immunity vary from site to site.
Proliferative lesions occur when there is a small bacillary load and the host cellular
immune responses dominate. Tubercles are compact, with admixed activated macrophages admixed surrounded by proliferating lymphocytes, plasma cells, and an outer
rim of fibrosis. Intracellular killing of mycobacteria is effective, and the bacillary load
remains low. When large numbers of bacilli are present and host defenses are
weak, then exudative lesions predominate. These loose aggregates of immature macrophages, neutrophils, fibrin, and caseation necrosis are sites of mycobacterial
growth. Untreated, these lesions progress and infection spreads.
EPIDEMIOLOGY
TB continues to reign as one of the world’s deadliest diseases. One-third of the
world’s population has been infected with TB.3,4 In the United States, there are an estimated 9 million people with LTBI.5,6 Worldwide in 2011, there were approximately 1.4
million TB-related deaths. Among HIV-infected individuals, TB is the leading cause of
death. Foreign-born individuals are 10 times more likely to be infected with TB than
those born in the United States. In the United States, the rate of TB is declining.4
Tuberculosis 745
TRANSMISSION
TB transmission occurs via inhalation of droplet nuclei. Person-to-person transmission continues to present significant public health issues as work continues toward
decreasing the spread of TB. Individuals with undiagnosed active untreated pulmonary or laryngeal disease are contagious, particularly when cavitary disease is present
or when the sputum is AFB smear positive.7 Likewise, patients with sputum smearnegative, culture-positive pulmonary TB can also transmit infection. In immonocompetent individuals, TB can remain in an inactive (dormant) state for years without
causing symptoms or spreading to other people.8 Only individuals with active TB
can spread the disease. Isolated extrapulmonary TB is not contagious, although
such patients require careful evaluation for pulmonary or laryngeal TB.9 Immunocompromised patients with extrapulmonary TB should be presumed to have pulmonary TB
until proved otherwise with negative sputum samples, even if chest radiography is
normal.10
SCREENING/DIAGNOSES
The CDC recommends that high-risk populations in the United States are screened for
latent infection, including HIV patients, IV drug users, health care workers who serve
high-risk populations, and contacts of individuals with pulmonary TB.11 The US Preventive Services Task Force recommends routine screening for TB in high-risk populations.12 The goal of this recommendation is to identify persons at significant risk for
progressing to active disease. A validated risk-assessment questionnaire may be
used to identify children who are likely to benefit from screening. Screening persons
other than high-risk populations places a burden on resources and is, therefore, not
recommended.13
TST and IGRA are the standard methods for identifying persons infected with the
mycobacterium.14 All individuals with positive screens and suspicious for active infection should have a chest radiograph, 3 sputum samples obtained for AFB, nucleic acid
amplification test (NAAT), complete blood cell count, and electrolytes (eg, sodium). If a
patient is unable to spontaneously produce sputum, it should be induced (with appropriate precautions to prevent transmission) or obtained via a gastric aspirate. Stained
smears should be made from sputum specimens to identify AFB, because this is the
first bacteriologic evidence of infection and gives an estimate of how infectious a patient is.15 If AFBs are seen on smear, therapy should be started and patients maintained in isolation.
Sputum culture may also be used for diagnosis of TB. It is more sensitive than smear
staining, facilitates identification of the mycobacterium species by nucleic acid hybridization or amplification, and evaluates drug sensitivity. Limitations of sputum culture
are dependent on the medium used to culture mycobacterium. Cultures may take 4
to 8 weeks to get results.
NAAT performed on at least one respiratory specimen may also be used as a diagnostic tool.14 NAAT may speed the diagnosis in smear-negative cases or in patients
with other strains of mycobacterium. Genotyping is expensive and best used when
there are TB outbreaks. Finally, patients with positive TB tests should also be tested
for HIV within 2 months of diagnosis.
One of the diagnostic challenges is secondary to accurate testing; 40% to 50% of
TB cases are AFB smear negative and 15% to 20% have negative cultures. If there is a
strong clinical suspicion of active TB, especially when accompanied by a positive skin
test, empiric TB therapy may be tried before laboratory confirmation of infection. In
746 Cruz-Knight & Blake-Gumbs
patients with low suspicion for active TB and smears negative for AFB, it is acceptable
to wait for the results of AFB culture or repeat chest radiograph before starting
treatment.
The TST or IGRA helps diagnose LTBI in a person exposed to MTB but without signs
of active TB.16 The TST and IGRA measure the response of T cells to TB antigens.
Because false-negative results occur in 20% to 25% of patients with active pulmonary
TB, these tests should not be used alone to exclude a diagnosis of active TB.17 Immunocompetenceand vaccination status may affect interpretation of the TST. Induration of
greater thanor equalto 15 mm in diameter is a positive test in an immunocompetent person.18 Immunocompromised individuals may require a 2-step testing approach at least
2 weeks apart to prime the immune system. In this subset of patients, induration of
greater than or equal to 10 mm is considered a positive test. In individuals with a history
of bacille Calmette-Gue ´ rin, vaccination and IGRA are preferred due to superior specificity. IGRA is also used for patient subsets at high risk of TB but low adherence with
TB testing, requiring a 48- to 72-hour confirmatory reading, as in the case of the TST.13
The CDC and American Thoracic Society recommend targeted testing for LTBI in
high-risk groups, such as people with HIV, IV drug users, health care workers who
serve high-risk populations, and contacts of individuals with pulmonary TB. Patients
receiving tumor necrosis factor a antagonist should be tested before initiation of
therapy.
CLINICAL MANIFESTATION
TB may clinically manifest as primary TB, reactivation TB, laryngeal TB, endobronchial
TB, lower lung field TB infection, and tuberculoma. Clinical manifestations of TB vary
according to site of mycobacterial proliferation.13 The most common route of entry of
MTB is through the bronchial system. Patients with pleural TB may present with a
chronic cough, night sweat, pleurisy, blood-tinged sputum, and weight loss.19,20 TB
initial presentation may mimic other medical conditions. The table below highlights
the common clinical presentations of TB.
Clinical Presentations of Tuberculosis
Site of Organism Proliferation Clinical Symptoms
Pleural TB Blood-tinged sputum producing chronic cough, pleurisy,
chest pain
TB lymphadenitis Enlarged cervical or supraclavicular lymphnodes
Tuberculous meningits Persistent or intermittent headach for 2–3 weeks. Mental
status changes, coma
Skeletal TB Spine is most common site (Pott disease). Back pain,
stiffness, lower extremity paralysis (50%) occurrence
Tuberculous arthritis Involves on joint. Hips and knees more commonly affected.
Pain precedes radiographic changes
Genitourinary TB Flank pain, dysuria, and frequent urination. Men may
present with painful scrotal mass, prostatitis, orchitis, or
epididymitis. In women, condition may mimic pelvic
inflammatory disease. 10% of sterility in women
worldwide and 1% of women in industrialized countries
Gastrointestinal TB TB may infect any site along the gastrointestinal tract. TB
can manifest as nonhealing ulcers of the mouth or anus,
difficulty swallowing, abdominal pain (peptic ulcer like),
malabsorption, pain diarrhea, or hematochezia
Tuberculosis 747
Patients with TB lymphadenitis most commonly present with enlarged lymph nodes
in the cervical and supraclavicular areas.21 There can be unilateral or bilateral involvement. In patients suspected of having TB with superficial lymphadenitis, the first diagnostic test should be fine-needle aspiration. For questionable diagnosis, lymph node
excisional biopsy should be obtained. In patients with skeletal TB, approximately 70%
have a positive tuberculin skin test.22 In skeletal TB, pain of the involved area is the
most common complaint with absent constitutional symptoms. Because onset of
symptoms is gradual, diagnosis is frequently delayed. Patients may present with lower
extremity paralysis or limited movement with local swelling. Patients may also present
with a nontender abscess. When a diagnosis of TB arthritis/skeletal TB is in question,
then synovial biopsy or tissue biopsy is the diagnostic modality. Although fluid/tissue
cultures may be positive in up to 80% of cases, AFB smear is a poor diagnostic
modality.23
Patients with central nervous system TB and meningitis or intracranial tuberculomas
(rounded mass lesions can develop during primary infection or when a focus of reactivation TB becomes encapsulated) may present with headache, neck stiffness,
altered mental status, and cranial nerve abnormalities.24 Cerebrospinal fluid examination is essential for diagnosis of TB meningitis. Rapid diagnosis leads to improved outcomes but depends on a high level of suspicion, especially in industrialized
medicine.25 AFB culture of cerebrospinal fluid is definitive modality for diagnosis,
whereas cerebrospinal fluid analysis is usually normal. Because awaiting cultures
may present a delay in cure, treatment is initiated presumptively based on clinical suspicion, risk factors, and cerebrospinal fluid results. Approximately 50% of patients
with central nervous system TB have chest radiograph abnormalities consistent
with pulmonary TB; head CT or MRI may show tuberculomas or signs of intracranial
pressure.26
In abdominal TB, the TST is positive 70% of the time with radiographic evidence of
LTBI.27 Patients may present with abdominal swelling (ascites), abdominal pain, fever,
and/or change in bowel habits. Diagnosis is based on culture growth from ascetic fluid
or biopsy. TB enteritis presents most commonly with ileocecum involvement, followed
by ileum, cecum, and ascending colon. Patients most commonly present with chronic
abdominal pain. Changes in bowel habits are usually present along with heme-positive
stool. Emergency clinical presentations may be due to small bowel obstruction or a
right lower quadrant mass. Peritoneal fluid culture is 92% sensitive but results may
take up to 8 weeks. Peritoneal biopsy may reveal military nodules over the peritoneum
and lead to presumptive diagnosis in 80% to 95% of patients. TB enteritis is best diagnosed by colonoscopy and biopsy, which may reveal ulcers, pseudopolyps, or
nodules.
Genitourinary TB may present as dysuria, hematuria, and urinary frequency.28
Although symptoms may be absent in up to 30% of patients, men may present with
a scrotal mass and women may present with pelvic inflammatory disease–like symptoms.29,30 Constitutional symptoms are rare. Diagnosis is often delayed, leading to
kidney involvement. Chest radiograph is abnormal in 40% to 75% of patients, with
positive skin test in up to 90% of patients.31 Diagnosis depends on culturing TB
from morning urine samples (3 are recommended) or biopsy of a lesion seen on cystoscope or other imaging modalities. Urine culture for TB may be positive in 80% of patients; 3 samples for culture improve sensitivity; this requires a high level of suspicion.
The classic finding of sterile pyuria is neither sensitive nor specific. Definitive diagnosis
of genital TB is based on tissue biopsy.32
Pericardial TB is rare but may present with chest or pleurisy and cardiac effusion on
imaging. Chest radiograph shows cardiomegaly (up to 95% of cases) and pleural
748 Cruz-Knight & Blake-Gumbs
effusion (approximately 50%) with low-voltage ECG occurring 25% of the time.
T-wave inversion is common in approximately 90% of patients. Diagnosis requires
pericardial fluid or biopsy. AFB smear is commonly negative; cultures are positive
only 50% of the time; biopsy leads to a higher diagnostic yield.
Patients presenting with full-blown constitutional symptoms and a diagnosis of TB
should be evaluated for disseminated TB.33 The diagnosis is based on the number of
organs involved. The most common organs are lungs, liver, spleen, kidneys, and bone
marrow. Chest radiograph (if nondiagnostic, consider a chest CT), sputum for AFB
smear and culture, blood culture for mycobacteria, and first morning void urine for
AFB should be obtained.34 Lumber puncture and biopsy of superficial lymph nodes
may be done based on clinical presentation. Sputum smear is positive in one-third
of patients, with culture positive in approximately 60%. TST is positive in only 45%
of patients with disseminated disease. Prompt diagnosis of disseminated TB is necessary to improve clinical outcome.
Elderly individuals with TB may not display typical signs and symptoms of TB infection due to poor immunogenicity. Active TB infection in this age group may manifest as
nonresolving pneumonitis. Likewise, signs and symptoms of extrapulmonary TB may
be nonspecific and include leukocytosis, anemia, and hyponatremia due to the release
of antidiuretic hormone–like hormone from affected lung tissue.
RADIOGRAPHIC MANIFESTATION
Primary pulmonary TB is often accompanied by a normal chest radiograph. Hilar
adenopathy is the most common chest abnormality. There are studies showing a
65% occurrence of cases.35 Hilar changes can occur within a week after skin test conversion or in the span of 2 months. In most cases, these findings often resolve within
the first year of detecting a positive skin test for primary TB.
Another study showed one-third of the 517 converters developed pleural effusions,
within the first 3 to 4 months after infection but occasionally as late as 1 year.36 Pulmonary infiltrates were documented in 27% of patients.37 Perihilar and right-sided infiltrates were the most common, and ipsilateral hilar enlargement was the rule.
Although contralateral hilar changes sometimes were present, only 2% of patients
had bilateral infiltrates. Lower and upper lobe infiltrates were observed in 33% and
13% of adults, respectively; 43% of adults with infiltrates also had effusions. Most infiltrates resolved over months to years. In 20 patients (15% of cases), however, the infiltrates progressed within the first year after skin test conversion, so-called
progressive primary TB. The majority of these patients had progression of disease
at the original site, and 4 developed cavitation.38
In studies looking at culture positive, the most common radiologic finding was hilar
lymphadenopathy, present in 67% of cases.39 Right middle lobe collapse may complicate the adenopathy but usually resolves with therapy.
Several factors probably favor involvement of the right middle lobe39:
Dense lymph nodes
Longer length and smaller internal caliber
Sharper branching angle
Pleural effusions are also common in active TB infection. A Canadian retrospective study demonstrated pulmonary infiltrates in 63% of patients, and 85% of infiltrates were in the midlung to lower lung fields.40 Two patients had cavitation and
2 others evidence of endobronchial spread. A majority of patients with reactivation
TB have abnormalities on chest radiography. Reactivation TB typically involves the
Tuberculosis 749
apical-posterior segments of the upper lobes (80%–90% of patients), followed in
frequency by the superior segment of the lower lobes and the anterior segment of
the upper lobes.41
Atypical radiographic patterns may occur in up to 30% adults with reactivation TB.
Findings may include hilar adenopathy, infiltrates or cavities in the middle or lower lung
zones, pleural effusions, and solitary nodules. Atypical findings are seen more often in
the setting of primary TB. Ironically, approximately 5% of patients with active TB present with upper lobe fibrocalcific changes thought to be indicative of healed primary
TB. In the setting of pulmonary symptoms, these patients should be evaluated for
active TB. A normal chest radiograph is also possible even in active pulmonary TB.
CT scanning of chest is more sensitive than plain chest films for diagnosis, with higher
sensitivity for smaller lesions located in the apex of the lung.42 CT scan may demonstrate a cavity or apicoposterior infiltrates, cavities, pleural effusions, fibrotic lesions
causing distortion of lung parenchyma, elevation of fissures and hila, pleural adhesions,
and formation of traction bronchiectasis. To detect early bronchogenic spread, highresolution CT is the imaging technique of choice. The most common findings consist
of centrilobular 2-mm to 4-mm nodules or branching linear lesions representing intrabronchiolar and peribronchiolar caseation necrosis. MRI detects intrathoracic lymphadenopathy, pericardial thickening, and pericardial and pleural effusions.
Currently, there is no role for routine use of positron emission tomography (PET) for
evaluation of TB. PET uptake of fludeoxyglucose F 18 (FDG) does not differentiate
infection from tumor, but the macrophages in active TB do not proliferate and do
not need choline C 11, resulting in low choline C 11 uptake; this in contrast to the macrophages in malignancy. Therefore, the combination of a high FDG and low choline C
11 uptake on PET may be useful but not diagnostic of TB.
Tuberculous infection of the tracheobronchial tree can develop from direct extension to the bronchi from a parencymal focus. This happens from infected sputum
that leads to spread of MTB. The lesions are seen in the main and upper bronchi.
Five percent of the time the lower trachea is involved. Endobronchial TB has been
described in 10% to 40% of patients with active pulmonary TB. Bronchial stenosis
is observed in 90% of cases not receiving early diagnosis to prevent development
of fibrosis.
TREATMENT
Treatment of TB depends on whether LTBI or active TB is treated. If a patient has had
recent close contact with a person with active TB but is still in the 12-week window
where TST may be negative, immediate LTBI treatment should be considered if the
patient is at high risk of progression to active TB or has increased susceptibility to disease.43 In patients with significant exposure with active TB repeat, TST should be performed 12 weeks after contact has ended, and treatment should be continued if the
TST result is positive or discontinued if the result is negative. The exception to this
recommendation is that persons who are immunocompromised, including those
with HIV infection, who had contact with individuals with active TB should continue
treatment of LTBI, even if repeat TST is negative.
Initial empiric treatment of MTB consists of a 4-drug regimen: isoniazid, rifampin,
pyrazinamide, and either ethambutol or streptomycin.44 Once the MTB isolate is
known to be fully susceptible, ethambutol (or streptomycin, if it is used as a fourth
drug) can be discontinued.45 Patients diagnosed with active MTB should undergo
sputum analysis for MTB weekly until sputum conversion is documented. Treatment
duration is typically 6 to 9 months.
750 Cruz-Knight & Blake-Gumbs
Pyrazinamide may be stopped after 2 months of treatment of a proved susceptible
isolate. Isoniazid plus rifampin must be continued for an additional 4 months. If isolated isoniazid resistance is proved, isoniazid should be stopped and rifampin, pyrazinamide, and ethambutol should be continued for the entire 6 months. It is
necessary to extend therapy if the patient has cavitary disease and/or remains
culture-positive after the first 2 months of treatment.
Patients receiving pyrazinamide should undergo baseline and periodic serum uric
acid assessments, and those receiving long-term ethambutol therapy should undergo
baseline and periodic visual acuity and red-green color perception testing (ie, the Ishihara test for color blindness). Monitoring for toxicity includes baseline and periodic
liver enzymes, complete blood cell count, and serum creatinine.
The development of drug resistance to 1 or more drugs by MTB is a major concern
worldwide. Typically, drug resistance results from spontaneous mutations within the
MTB DNA. Strains of drug-resistant MTB (DR-MTB) were first demonstrated after
streptomycin was introduced as a treatment in 1944.46 Rates of drug resistance are
highest in cases where previous treatment has occurred, especially when treatment
has been incomplete due to either poor adherence or inadequate therapeutic regimen.
Currently, 17% of newly diagnosed MTB cases are resistant to 1 or more first-line
agents. Isoniazid is the drug most commonly associated with resistance (10%), but
MTB strains can develop resistance to any medication or combination of medications.47 Strains resistant to both isoniazid and rifampin, the 2 most effective currently
available drugs, and possibly resistant to other drugs are called multidrug resistant
(MDR) and were first reported on in the early 1980s. MDR cases are now found worldwide. In 2009, WHO estimated that there were 440,000 new MDR-TB cases or 3.3% of
new TB cases were MDR.49 Annual mortality from MDR-TB was estimated to be
Box 1
High-risk populations needing targeted tuberculin testing and treatment of latent infection
Persons at high risk of exposure to and infection with MBT
Persons in close contact with someone who has confirmed active TB
Foreign-born persons from endemic countries who have been living in the United States for
5 years or less (especially children younger than 4 years)
Residents and employees of congregate settings (eg, correctional facilities, long-term care
facilities, and homeless shelters)
Health care workers with high-risk patients
Medically underserved, low-income populations
Infants, children, and adolescents exposed to adults in high-risk categories
Persons at high risk of progression from LTBI to active disease
Persons with HIV infection
Persons recently (within the past 2 years) infected with MTB
Children younger than 4 years
Patients who are immunosuppressed (eg, those with diabetes, chronic or end-stage renal
disease, silicosis, cancer, malnutrition, prolonged steroid use, or organ transplants; those taking
tumor necrosis factor a inhibitors)
Data from Potter B, Rindfleisch K, Kraus CK. Management of active tuberculosis. Am Fam Physician 2005;72(11):2225–32.
Tuberculosis 751
150,000 worldwide.48 Inadequate treatment of MDR-TB leads to treatment failure,
increased mortality, and the creation of MTB strains with an even more complex resistance profile.
Directly observed therapy short-term (DOTS) programs increase the likelihood of
adherence and treatment completion and reduce the risk of the development of
DR-MTB and extensively drug-resistant TB (XDR-TB).49 DOTS is recommended for
all patients diagnosed with MTB, whether drug-resistant or susceptible. With DOTS, patients on the regimens (discussed previously) can be placed on 2- to 3-times per week
dosing after an initial 2 weeks of daily dosing. Patients on twice-weekly dosing may not
miss any doses. Prescribe daily therapy for patients on self-administered medication.
Treatment recommendations for MDR-TB consist of an intensive 8 months of treatment that includes pyrazinamide and a minimum of 4 additional effective second-line
drugs, including a fluoroquinolone (not to include ciprofloxacin), an injectable antibiotic
(either kanamycin, amikacin, capreomycin, or viomycin, but not streptomycin, which is
considered a first-line drug), a thioamide (either ethionamide or prothionamide), and
Table 1
Currently available antituberculosis drugs
Group 1: first-line oral anti-TB drugs Isoniazid (H)
Rifampin or rifampicin (R)
Ethambutol (E)
Group 2: injectables Pyrazinamide (Z) rifabutin (Rfb)
Kanamycin amikacin
Capreomycin streptomycina
Group 3: fluoroquinolones Levofloxacin moxifloxacin
Ofloxacin
Gatifloxacin
Group 4: oral bacteriostatic
second-line drugs
Ethionamide
Protionamide
Cycloserine terizidone
Group 5: anti-TB drugs with
unclear efficacy or role
p-Aminosalicylic acid clofazimine linezolid
Amoxicillin/clavulanate thioacetazone
Clarithromycin imipenem
a Considered a first-line drug.
Table 2
Treatment options for latent tuberculosis infection
Drug
Daily Dosage
(Maximum)
Adult Intermittent
Dosage (Maximum) Duration
Isoniazid 5 mg per kg
(300 mg)
15 mg per kg
(900 mg per dose)
twice per week
Nine months in adults and children
(6 mo may be an alternative
treatment duration in adults)
Rifampin
(Rifadin)
10 mg per kg
(600 mg)
10 mg per kg
(600 mg per dose);
daily dosing required
when used alone
Four months in adults; 6 mo in
children
Note: Rifampin plus pyrazinamide is no longer recommended for the treatment of LTBI.
Rifampin plus isoniazid (same dosing) for 3 months may be an alternative treatment option in
select patients, but risk of hepatotoxicity may increase.
Data from World Health Organization. Treatment of tuberculosis: guidelines for national programmes. 4th edition. 2010. Available at: http://www.who.int. Accessed January 24, 2013.
752 Cruz-Knight & Blake-Gumbs
Table 3
Adverse effects of antituberculin drugs
Drug Main Adverse Effects Monitoring Parameters
Isoniazid Hepatotoxicity
Lupus-like syndrome
Peripheral neuropathy
Monitor LFTs and for flushing and decreased sensation in extremities LFTs should be
monitored monthly in patients who are at a higher risk of hepatotoxicity, have
preexisting liver disease, or develop abnormal LFTresults. LFTs should also be checked
in patients who develop clinical symptoms of hepatitis; isoniazid should be
discontinued if findings on LFTs increase by more than 5 times the upper limits of
normal in patients without symptoms of hepatotoxicity and by more than 3 times the
upper limits of normal in patients with symptoms.
Monoamine toxicity If flushing occurs, patients should be counseled to avoid foods with high
concentrations of monoamines (eg, aged cheeses, wine).
Rifampin (Rifadin) Drug interactions
Hepatotoxicity
Immunologic reactions
Orange discoloration of body fluids
Baseline laboratory tests (including complete blood cell count and serum creatinine
measurements) and monthly; every-other-month; or 1-, 3-, or 6-mo monitoring of
LFTs and clinical symptoms are acceptable for most patients but not required. LFTs
should be monitored monthly or twice monthly in patients who are at a higher risk of
hepatotoxicity, have preexisting liver disease, or develop abnormal LFT results.
Acute renal failure
Influenza-like symptoms
Hemolytic anemia, thrombocytopenia (with potential for acute renal failure)
Pruritus (with or without rash)
Patients should be counseled about the risk of contact lens discoloration.
Pyrazinamide Arthralgias
Gastrointestinal upset
Hepatotoxicity
Rash
Baseline LFTs; serum creatinine may be assessed at baseline for dosing adjustments. LFTs
should be monitored monthly or twice monthly in patients who are at a higher risk of
hepatotoxicity or who have underlying hepatic dysfunction.
Hyperuricemia Check uric acid levels if patient is symptomatic
Ethambutol (Myambutol) Optic neuritis Baseline and monthly testing of visual acuity and color discrimination; serum creatinine
may be assessed at baseline for dosing adjustments.
Abbreviation: LFT, liver function test.
Data from Potter B, Rindfleisch K, Kraus CK. Management of active tuberculosis. Am Fam Physician 2005;72(11):2225–32.
Tuberculosis 753
cycloserine or teridizone.50 Treatment should be continued for a minimum of 20 months
with 4 effective medications. The injectable antibiotic may be discontinued after
completion of 8 months of therapy.
XDR-TB is a rare type of MDR-TB that is resistant to isoniazid and rifampin, plus any
fluoroquinolone and at least 1 of 3 injectable second-line drugs (ie, amikacin, kanamycin, or capreomycin).43 Because XDR-TB is resistant to the most potent MTB
drugs, patients are left with treatment options that are much less effective. XDR-TB
is of special concern for persons with HIV infection or other conditions that can
weaken the immune system. These persons are more likely to develop TB disease
once they are infected and, moreover, have a higher risk of death once they develop
TB. See Box 1 and Tables 1–3 for outline of antituberculosis drugs.
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22. Oursler KK, Moore RD, Bishai WR, et al. Survival of patients with pulmonary
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24. Miller LG, Asch SM, Yu EI, et al. A population-based survey of tuberculosis
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25. Moon MS, Kim SS, Lee BJ, et al. Spinal tuberculosis in children: retrospective
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27. Lin YL, Fan YC, Cheng CY, et al. The case j Sterile pyuria and an abnormal
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29. Madeb R, Marshall J, Nativ O, et al. Epididymal tuberculosis: case report and
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30. Wise GJ, Shteynshlyuger A. An update on lower urinary tract tuberculosis. Curr
Urol Rep 2008;9(4):305–13.
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tuberculosis in adults. Confusion with reinfection in the pathogenesis of chronic
tuberculosis. Ann Intern Med 1968;68:731.
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in patients with a normal chest radiograph. Chest 1999;115:445.
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756 Cruz-Knight & Blake-Gumbs

Preclinical Rheumatoid
Arthritis: Identification,
Evaluation, and Future
Directions for
Investigation
Kevin D. Deane, MDa,*, Jill M. Norris, MPH, PhDb,
V. Michael Holers, MDa
‘‘When the rheumatic poison is in the system, any disturbing circumstance, even
of temporary duration, such as over fatigue, anxiety, grief or anger, by rendering
the system more susceptible of its influence, may prove the accidental or exciting
cause of the disease’’
Henry William Fuller in ‘‘On Rheumatism, Rheumatic Gout, and Sciatica’’
Publishers: Samuel S & William Wood, New York, 1854.
The discovery of genetic and environmental factors associated with rheumatoid
arthritis (RA), and elevations in autoantibodies and inflammatory markers prior to
the onset of symptomatic disease, coupled with similar findings in other autoimmune
diseases including type 1 diabetes mellitus (T1DM), has led to the creation of a shared
model of autoimmune disease development. In this model, the development of RA
follows a natural history divided into phases wherein genetic and environmental interactions initially lead to a period of asymptomatic autoimmunity, evidenced by the
presence of RA-related autoantibodies, that later evolves into clinically apparent
disease. It is the initial phases of risk and asymptomatic autoimmunity that encompass
‘‘preclinical’’ RA.
To understand the genetic and environmental influences that are important to the
evolution of RA, as well as develop predictive models and preventive strategies for
a Division of Rheumatology, University of Colorado School of Medicine, 1775 Aurora Court,
Mail Stop B-115, Aurora, CO 80045, USA
b Department of Epidemiology, Colorado School of Public Health, University of Colorado,
13001 East 17th Place, Aurora, CO 80045, USA
* Corresponding author.
E-mail address: Kevin.Deane@UCDenver.edu
KEYWORDS
Rheumatoid arthritis Preclinical period
Anticyclic citrullinated peptide antibodies
Rheum Dis Clin N Am 36 (2010) 213–241
doi:10.1016/j.rdc.2010.02.001 rheumatic.theclinics.com
0889-857X/10/$ – see front matter ª 2010 Elsevier Inc. All rights reserved.
future symptomatic disease, this preclinical period must be investigated. Herein are
discussed the following issues related to preclinical RA: (1) what is known about the
preclinical development of autoimmunity and inflammation in RA as well as other autoimmune diseases that may follow a similar model of development as RA, (2) how RA
development can be modeled based on studies in preclinical RA and other autoimmune diseases, (3) practical issues related to the challenge of defining for research
studies ‘‘preclinical’’ RA, as compared with clinically apparent disease, and (4) what
aspects of RA evolution including genetic and environmental influences, and predictive and preventive models, could be addressed in studies of the preclinical period.
Finally, potential methodologies and areas of focus going forward for research into
preclinical RA are discussed.
PART 1. AUTOANTIBODIES AND INFLAMMATION IN PRECLINICAL RHEUMATOID
ARTHRITIS AS WELL AS OTHER AUTOIMMUNE DISEASES
Studies of Preclinical Rheumatoid Arthritis
Multiple studies have shown that RA-related autoantibodies are present years before
the diagnosis of RA (Table 1).1–11 del Puente and colleagues,1 who investigated RA in
the Pima Indians in the Southwestern United States, showed that rheumatoid factor
was present before the onset of clinically apparent RA. Aho and colleagues,2,12–14
who investigated preclinical RA in Finland using a biobank of stored prediagnosis
samples, and Jonsson and colleagues,15 who used Icelandic biobank samples, also
demonstrated that rheumatoid factor (RF) (by various methodologies) was present
prior to the onset of clinically apparent RA. Also, in a prospective study of initially
healthy family members of patients with RA, Silman and colleagues11 showed that
the presence of RF preceded the onset of clinically apparent RA.
Later studies also showed preclinical RA positivity for RF, as well as positivity for
the highly RA-specific antibodies to citrullinated protein antigens (ACPAs). Again
using a Finnish biobank, Aho and colleagues3,4 demonstrated preclinical RA positivity
of antikeratin (AKA) and antiperinuclear factor (APF) antibodies, and antifillagrin antibodies (AFA)6—autoantibody targets that, based on later findings, represented citrullinated antigens.16 Using stored blood samples available through the Medical
Biobank of Northern Sweden, Rantapaa-Dahlqvist and colleagues7 evaluated for
elevations of RF isotypes (immunoglobulins [Ig] M, G and A) and the anticyclic citrullinated peptide (anti-CCP) antibody in 98 preclinical samples from 83 RA patients,
collected a median of 2.5 years prior to symptomatic disease onset. In this study,
approximately 34% of patients were positive for anti-CCP within 1.5 years prior to
diagnosis of RA, and the prevalence of RF isotype positivity ranged from about
17% to 34% during this same period. In addition, in comparison to controls, a combination of both anti-CCP and any RF isotype was highly specific (99%) for the future
development of classifiable RA. This report was followed by a similarly designed
retrospective cohort study by Nielen and colleagues8 that evaluated preclinical RA
RF and anti-CCP positivity using pre-RA diagnosis samples stored in a Dutch blood
donor biobank. In this study, 79 RA patients with stored prediagnosis samples were
identified, with a median of 13 preclinical samples per case. Of these 79 cases,
approximately 28% and 41% had pre-RA diagnosis elevation of RF (IgM isotype) or
anti-CCP, respectively. RF was positive a median of 2.0 years prior to RA diagnosis
(range 0.3–10.3 years), and anti-CCP was positive a median of 4.5 years prior to
RA diagnosis (range 0.1–13.8 years).
Additional studies using stored biobank samples have also demonstrated preclinical
RA positivity for autoantibodies. Using stored pre-RA samples from 83 United States
214 Deane et al
military subjects with RA, Majka and colleagues9 demonstrated pre-RA diagnosis positivity for RF and anti-CCP. In addition, they demonstrated that individuals that were
older at the time of diagnosis of RA had longer duration of preclinical positivity of autoantibodies, a finding that was supported by work by Bos and colleagues.17 Chibnik and
colleagues18 utilized the Nurses’ Health Study (NHS) biobank to demonstrate anti-CCP
positivity prior to RA diagnosis, and showed that a lower cut-off value for anti-CCP than
the kit suggested was also highly specific for future RA.
Multiple studies have also evaluated elevations of inflammatory markers prior to
diagnosis of RA, with varying results (see Table 1).19–24 In their Finnish biobank study,
Aho and colleagues25 found no significant elevation of C-reactive protein (CRP) in preRA diagnosis samples, although the time of sample collection prediagnosis was not
reported. Using the same Medical Biobank of Northern Sweden as in the study of
pre-RA RF and anti-CCP positivity, Rantapaa-Dahlqvist and colleagues21 showed
a significant elevation of monocyte chemoattractant protein-1 (MCP-1) in 92 pre-RA
cases versus controls, but not secretory phospholipase A2 (sPLA2), high-sensitivity
CRP (hsCRP) or interleukin (IL)-6. Nielen and colleagues19 demonstrated, in the Dutch
pre-RA sample cohort described above, that CRP was elevated in the pre-RA period,
most commonly about 2 years before diagnosis, regardless of prediagnosis autoantibody positivity, although these investigators were unable in this study to demonstrate
the chronologic sequence of appearance of CRP versus autoantibodies. Nielen and
colleagues20 later additionally demonstrated pre-RA elevation of sPLA2 in this cohort,
but were unable to determine whether CRP or sPLA2 preceded autoantibodies in the
preclinical period, and they concluded that the temporal development of autoantibodies and these 2 markers were probably similar. Jorgensen and colleagues24
utilized samples from a Norwegian biobank to examine in 49 cases with RA prediagnosis elevations of autoantibodies (RF and anti-CCP) and multiple cytokines. These
investigators found that RF and anti-CCP were elevated in RA cases prediagnosis;
however, they could not demonstrate any cytokine elevations prior to 5 years before
disease onset, and only tumor necrosis factor a (TNFa) was statistically significantly
elevated in cases (vs controls) during the 5-year period just before diagnosis of
RA.24 Using a single pre-RA diagnosis blood sample from 90 incident RA cases
(case status confirmed by chart review) identified in the Women’s Health Study
(WHS), Shadick and colleagues23 were unable to demonstrate significant elevations
in CRP levels in cases versus controls (with case samples available a mean of 6.6
years prior to diagnosis), and they were unable to use a single CRP level to predict
future RA. However, in a later study using 170 RA cases from a combination of the
NHS and WHS cohorts, the same group22 was able to demonstrate statistically significant elevations of soluble tumor necrosis factor receptor II (sTNFRII) prior to RA diagnosis, but not IL-6 or hsCRP. Most recently, Rantaapa-Dahlqvist and colleagues used
an expanded sample set from their Swedish Biobank, to demonstrate elevations of
multiple cytokines and chemokines prior to the diagnosis of RA, with these elevations
likely indicating pre-clinical RA activity of Th1, Th2, and T regulatory processes.26
There are caveats when interpreting the data regarding pre-clinical elevations of
biomarkers. Certainly the prospective studies by del Puente and colleagues1 and Silman and colleagues11 suggest that autoantibodies are truly elevated before the onset
of clinically apparent disease. However, in the studies of preclinical autoantibody and
inflammatory marker elevations using stored samples from biobanks, there were not
detailed joint-directed questionnaires or examinations performed at baseline or over
time to ensure that no clinically apparent arthritis was present at the time of presumed
preclinical RA blood collections. As such, it may be that the duration of pre-RA diagnosis autoantibody positivity is overestimated in the studies utilizing stored biobank
Preclinical Rheumatoid Arthritis 215
Table 1
Summary of selected studies of preclinical rheumatoid arthritis (RA)
Study Study Design
Biomarkers
Assessed Findings
Implications for Prediction
of Future RA
del Puente et al,
19881
Prospective; Native Americans,
Southwest United States
RF RF precedes diagnosis of RA Increased incidence of RA in RF1
individuals. Rates 2.4–48.3 per
1000 person-years, with highest
rates in those with highest RF
titers at baseline
Silman et al,
199211
Prospective; British; FDRs from
families with R2 RA cases
RF RF precedes diagnosis of RA Average incidence of RA 8 per
1000 person-years in FDRs;
highest rate in FDRs with RF1:
34.8 per 1000 person-years
Jonsson et al,
199215
Retrospective; Icelandic;
biobank
RF (isotypes) RF isotype elevations precede
diagnosis of RA
Not analyzed
Aho et al,
1985–19912,13,14
Retrospective; Finnish;
biobank
RF (isotypes) RF precedes diagnosis of RA Not analyzed
Aho et al,
1993, 20004,6
Retrospective; Finnish;
biobank
AKA, AFA, APF (later studies
showed target antigens
likely citrullinated)
AKA, AFA, APF precede
diagnosis of RA
RA-related antibodies may be
present in subjects who did not
develop RA in follow-up period
Rantapaa-Dahlqvist
et al, 20037
Retrospective; Swedish;
biobank; N 5 83 RA cases
RF, anti-CCP RF, anti-CCP precede diagnosis
of RA; 34% anti-CCP1 %1.5
years prior to RA diagnosis;
RF-isotypes1 in ~17%–34%
of cases pre-RA diagnosis
PPV 22%for future RA if RF-IgA
and anti-CCP positive (estimated
population prevalence of RA of
1%)
Nielen et al, 20048 Retrospective; Dutch;
biobank; N 5 79 RA cases
RF-IgM, anti-CCP RF-IgM, anti-CCP precede RA
diagnosis; 49% positive for
RF-IgM and/or anti-CCP pre-RA.
RF-IgM1 or anti-CCP1 median
of 2.0 or 4.8 years prior to
diagnosis of RA, respectively
PPV up to 100% for RA diagnosis
within 5 years based on 5-year
incidence rates of 0.001 (general
population) or 3.9% (estimated
from high-risk multicase RA
families)
216 Deane et al
Majka et al, 20089 Retrospective; United States
Military; biobank; N 5 83
RA cases
RF, anti-CCP Pre-RA diagnosis: RF1 57%
of cases, median 6.0 years;
anti-CCP1 61% of cases,
median 5.4 years
Increased age-at-diagnosis of RA
associated with longer duration
of preclinical autoantibody
positivity (replicated by Bos
et al17)
Rantapaa-Dahlqvist
et al, 200721
Retrospective; Swedish;
biobank
MCP-1, IL-6, CRP, sPLA2 After adjustment, only MCP-1
elevated prior to RA diagnosis
Not analyzed
Nielen et al,
2004, 200619,20
Retrospective; Dutch;
biobank
RF, anti-CCP, CRP, sPLA2 CRP and sPLA2 elevations precede
RA diagnosis; CRP ~2 years prior;
timing similar to RF/anti-CCP
Not analyzed
Jorgensen et al,
200824
Retrospective; Norwegian;
biobank; N 5 49 RA cases
RF-IgM, anti-CCP,
multiple cytokines
RF-IgM and/or anti-CCP precede
RA diagnosis by as much as 20
years; anti-TNF elevated <5 years
prior to diagnosis of RA. EBV
and Parvovirus serologies not
different between cases and
controls
Suggests that cytokine elevation
may indicate symptomatic
disease within 5 years
Berglin et al,
2004115
Retrospective; Swedish;
biobank; N 5 59 RA cases
RF, anti-CCP, HLA-DRB1
alleles *0404, *0401
Anti-CCP 1 DRB1*0404 or 0401
high-risk for future RA (OR ~67)
Johansson et al,
2006116
Retrospective; Swedish;
biobank; N 5 92 RA cases
RF, anti-CCP; PTPN22
(1858T)
Anti-CCP 1 PTPN22: 100% specific
for future RA, and high-risk
(OR >132)
Abbreviations: AFA, antifilaggrin antibodies; AKA, antikeratin antibodies; anti-CCP, anticyclic citrullinated peptide antibodies; APF, antiperinuclear factor antibodies; CRP, C-reactive protein; FDR, first-degree relative of proband with RA; HLA, human leukocyte antigen; IL-6, interleukin-6; MCP-1, monocyte chemoattractant protein-1; OR, odds ratio; PPV, positive predictive value; PTPN22, protein phosphatase 22; RF, rheumatoid factor; sPLA2, secretory phospholipase A2.
Preclinical Rheumatoid Arthritis 217
samples, as subjects may have had mild or fluctuating inflammatory symptoms long
before a confirmed diagnosis of RA. Also of importance, these pre-RA studies show
that not all RA patients have detectable pre-RA diagnosis autoantibody positivity.
Methodologic issues may in part explain these findings. For example, patients may
not have a stored blood sample available for analysis from the correct time period
to demonstrate their prediagnosis autoantibody positivity. Also, current assays for
autoantibodies may not detect the earliest preclinical autoantibody specificities;
perhaps an as-of-yet unknown citrullinated antigen is the earliest autoantibody target
in preclinical RA? In addition, not all patients with RA may develop detectable circulating autoantibodies in the preclinical period. For example, some patients may
develop circulating autoantibodies after clinically apparent disease develops. Of
note, in the Nielen study, while only about 28% of patients with RA were RF-positive
prediagnosis, about 67% of these same patients were positive for RF by 6 years post
diagnosis, suggesting that circulating RF develops in some cases after symptomatic
onset of RA.8 All of these issues will need to be considered in studies of preclinical
RA going forward.
The Contribution of Genetic and Environmental Factors Associated
with Rheumatoid Arthritis to Understanding Preclinical Development
Although the exact etiology of RA is unknown, there are multiple genetic and environmental factors that have been associated with disease. Estimates of the genetic
contribution to RA have ranged between 30% and 60%.27,28 Of the known genetic
factors associated with RA, a DRB1 allele containing the ‘‘shared epitope’’ is the
most important genetic factor associated with RA.29,30 Of the HLA alleles, HLADRB1*0401 and HLA-DRB1*0404 (within the HLA-DR4 group) are the most strongly
associated with RA, with an approximate relative risk for RA of almost 4 in Caucasians.31 In addition, several genes outside the HLA-DRB1 gene have recently been
associated with RA. These genes include PTPN22, TRAF1/C5, CTLA4, and STAT4,
and the list is rapidly growing.32,33
Several potential environmental factors that could play important roles in modifying
either susceptibility to RA or disease severity have been identified. High levels of
coffee consumption,34 in particular decaffeinated coffee,35 as well as a positive
smoking history,31,36 exposure to air pollution,37 and environmental exposure to
silica-containing dust38,39 are also associated with increased risk for RA. In addition,
infections have been associated with RA including pathogens such as the EpsteinBarr virus (EBV), Mycoplasma or Proteus species.27,40–43 Finally, several factors
have been identified as possibly protective against development of RA including
a history of successful pregnancy,44,45 oral contraceptive pill use,46–48 and higher
vitamin D intake.49
Several studies have examined the association of environmental factors with
asymptomatic RA-related autoantibody positivity. These studies suggest that lack
of oral contraceptive use and a history of heavy smoking are associated with an
increased prevalence of RF,50–52 whereas 25,hydroxyvitamin D levels are not associated with RF positivity in individuals without RA.53 Active pulmonary infection with
tuberculosis has also been associated with RF and anti-CCP positivity in individuals
without clinically apparent synovitis.54,55 These studies suggest that environmental
factors affect RA-related autoimmunity, although prospective evaluation of future
risk for RA in these types of autoantibody positive subjects is lacking.
Of recent interest regarding the pathogenesis of RA are interactions between
genetic and environmental factors that may lead to RA-related autoimmunity and
disease. For example, several studies have reported that smoking in individuals with
218 Deane et al
specific HLA alleles is associated with ACPA-positive RA, suggesting that a geneenvironment interaction leads to RA-related autoimmunity.56–59
However, while genetic and environmental factors have been associated with RA,
the exact role that these factors play in the development of RA-related autoimmunity
is not yet clear. Also, it is unclear whether these factors may lead to initial RA-related
immune dysregulation or transition from asymptomatic autoimmunity to clinically
apparent RA. It is important that, as discussed later, prospective study of the early
phases of RA development should help to clarify these issues.
Preclinical Studies in Other Autoimmune Diseases
In addition to the information about preclinical RA available from RA-specific studies,
much about the evolution of autoimmunity can be learned by examining the preclinical
natural history of other autoimmune diseases including T1DM and systemic lupus
erythematosus (SLE). In particular, prospective studies of T1DM have led to the development of a model of disease evolution that may be of importance to RA.
T1DM results from autoimmune-mediated destruction of the pancreatic b cells, and
it affects approximately 1 in 300 children. Numerous studies of T1DM have established
that there are specific high-risk HLA genotypes that predispose to disease.60,61 Moreover, the autoimmune attack on the pancreatic b cells can be detected years before
clinical onset of T1DM via the presence of any of the T1DM-related autoantibodies
in the blood including antibodies to the following antigens: islet cell (ICA), insulin
(IAA), protein tyrosine phosphatase (IA2), and glutamic acid decarboxylase
(GAD65).62,63
Prospective studies of T1DM have established that T1DM exhibits several phases
during its development.63 The first phase is defined as the presence of genetic risk
factors that, either alone or in combination, may predispose to the loss of self tolerance. The second phase is reached when transformation from the risk state to a state
of immunologic autoreactivity occurs; this second phase of ‘‘asymptomatic autoimmunity’’ is measurable by testing for T1DM-related biomarkers, but this phase is not
yet associated with the presence of clinically apparent hyperglycemia. This transition
from genetic risk to asymptomatic autoimmunity occurs either because of the introduction of an environmental factor, or perhaps because of the stochastic nature of
the immune response. In T1DM, this preclinical autoimmune phase is marked by initial
immune reactivity to only a small number of autoantigens. The third phase of T1DM is
the development of clinically apparent hyperglycemia; this final phase is characterized
immunologically by autoreactivity to numerous antigens and extensive immune-mediated tissue destruction of islet cells caused by many proinflammatory pathways.
The presence of these 3 phases of diseases in T1DM is well established, as is the
value of prospectively studying children with highly predictive autoantibodies in the
preclinical phases of disease for epidemiologic and genetic associations.60,64–70 Of
importance, due to the strong association of T1DM with b-cell (or islet) autoimmunity
(IA), defined as the presence of autoantibodies specific to b-cell autoantigens, IA has
become an alternative end point to clinically apparent hyperglycemia in T1DM
research. Advantages of this approach include the opportunity to study the pathologic
process underlying T1DM in a preclinical state, and to verify that a candidate risk
factor is not only related to diabetes but also to the alteration of immune function
preceding clinical onset of disease. Studies using as end points both autoimmunity
and clinically apparent diabetes have allowed for differentiation of the risk factors
that initiate humoral autoimmunity from those that promote progression from subclinical autoimmunity to diabetes.60,70 Of note, prospective studies using asymptomatic
IA as an outcome measure have identified important findings regarding dietary and
Preclinical Rheumatoid Arthritis 219
other factors in T1DM, including the lack of association of islet-cell autoimmunity with
childhood vaccines,68 and the important relationship of timing of cereal exposure
during the first year of life to the later development of IA.66 This latter finding has
been of importance in terms of potentially reducing risk for T1DM based on dietary
considerations.
The presence of autoantibodies can be also used in the prediction of future T1DM. In
first-degree relatives (FDRs) of diabetic individuals, the presence of a single autoantibody on one occasion has been found to have a sensitivity and specificity of 95%
and 99%, respectively, and a positive predictive value (PPV) of 46% for type 1 diabetes
with 5 years of follow-up.71 Of note, the number of unique T1DM-related autoantibodies
that are positive also predicts risk for future T1DM. For example, a person who tests
positive for multiple autoantibodies is at a much higher risk of developing T1DM than
a person with a single detectable autoantibody.72 However, T1DM-related autoantibodies may be transiently positive, and there are not yet enough longitudinal data to
determine if all people that develop autoantibodies will eventually develop
T1DM.63,72,73 Although not 100% predictive of future T1DM development, IA still serves
as a very useful intermediate end point when studying the autoimmune disease process
and potential risk factors for T1DM. In terms of RA, given the high specificity of certain
autoantibodies (notably ACPAs) for disease, using autoantibody positivity as a surrogate end point for autoimmunity in preclinical RA is likely to be of similar great value.
SLE is a multisystem autoimmune disease of unknown etiology. More than 98% of
SLE patients are positive for antinuclear antibodies (ANA) and many SLE patients have
additional reactivity to specific nuclear antigens including double-stranded DNA
(dsDNA), Smith, ribonuclear proteins, and Ro and La.74–77 Some of these autoantibodies are associated with specific clinical manifestations of disease. For example,
autoantibodies to dsDNA are associated with nephritis, and levels of anti-dsDNA antibodies may fluctuate in conjunction with disease activity.78,79 In addition, anti-Ro antibodies have also been shown to be associated with specific manifestations of SLE
including skin disease and neutropenia.75–77 Although these autoantibody systems
have been extensively studied for more than 50 years, the initiating events for the
development of these autoantibodies and the actual roles these antibody specificities
play in clinical SLE are not known. However, these SLE-related autoantibodies are
present in the serum of lupus patients many years prior to the first clinical evidence
of disease.80,81 Furthermore, the spectrum/number of autoantibody specificities
increases up to the time of diagnosis.82 The discovery of preclinical autoantibody positivity and evolution of antibody specificity has led to important investigations into
potential etiologic agents such as EBV infection in SLE, investigations that could not
be performed without preclinical studies.83
Animal Models and Preclinical Rheumatoid Arthritis
While animal models of arthritis are not an exact match to human disease, they have
provided important insights into the preclinical period of arthritis development. In
particular, investigations into the relationships between the major histocompatibility
complex (MHC) class II dependence of disease, a requirement in some instances
for the specific exposure to citrullinated autoantigen, and the timing between the
evolution of ACPA and clinically apparent arthritis have been helpful in understanding
important factors in preclinical arthritis. An early example was provided by evidence
that citrullinated proteins are found in the synovium after immunization with bovine
collagen type II in DBA/1j mice, a strain that is commonly used to study the type II
collagen-induced arthritis (CIA) model of RA.84 However, in this study no ACPAs
were detected. In a second study of the same model, ACPAs were found to develop
220 Deane et al
before clinically detectable joint inflammation.85 In this latter study, 2 methods were
used to show that the ACPAs are pathogenic: first, treatment of mice with a ‘‘tolerogenic’’ form of a citrullinated peptide decreased the arthritis disease severity by
approximately 60% and decreased the levels of ACPAs and epitope spreading to
other citrullinated peptides; and second, a mouse monoclonal antibody that recognized citrullinated peptides, and could be used as a representative example of an
ACPA, was found to greatly amplify joint inflammation. This process occurred only
following the administration of low doses of antibodies specific for type II collagen,
which induced the generation of citrullinated target antigens, presumably through
the actions of macrophages and neutrophils containing peptidyl arginine deiminase
(PAD) enzymes that participated in the inflammatory response. This second experiment suggested that, in the absence of citrullinated target antigens, there is no target
injury; however, when these antigens are present, such as during treatment with
monoclonal antibodies specific for type II collagen, ACPAs can greatly amplify inflammation and damage. Recently, additional monoclonal antibodies reactive with citrullinated type II collagen, with or without cross-reactivity to other epitopes, were also
found to amplify the development of arthritis in mice in vivo.86 In addition, another
study in rats has shown an increased incidence and severity of arthritis when collagen
type II is citrullinated before immunization.87
Other animal studies have focused on the relationship between cellular and humoral
autoimmunity to citrullinated antigens and the shared epitope and class II molecules.
For example, immunization with citrullinated vimentin peptide leads to CD41 T-cell
activation and proliferation in transgenic mice expressing human HLADRB1*0401.88 In addition, immunization of human HLA-DRB1*0401-transgenic
C57BL/6 mice with citrullinated human fibrinogen, but not native human fibrinogen
or either form of mouse fibrinogen, resulted in the development of arthritis in a substantial proportion of animals.89 In this setting, a relatively low level of inflammation was
present, but this was accompanied by specific antibody responses to citrullinated
human fibrinogen peptide, as well as T-cell responses to citrullinated protein.
ACPA-positive arthritis was also found to develop in mice that are immunized with
low doses of collagen type II and that have dysregulated MHC expression in the joints
owing to transgenic expression of class II transactivator.90 Finally, a particularly
intriguing study has recently shown that immunization of a subset of strains of mice
with human fibrinogen alone resulted in destructive arthritis as well as T- and B-cell
reactivity to fibrinogen.91 In this study, epitope spreading to citrullinated fibrinogen
as well as many synovial citrullinated and noncitrullinated autoantigens developed.
Remarkably, arthritis could be transferred to naı¨ve mice with either serum or fibrinogen-reactive T cells from immunized mice.
PART 2. THE PHASES OF RHEUMATOID ARTHRITIS DEVELOPMENT: FROM GENETIC
RISK TO CLINICALLY APPARENT DISEASE
Based on the above discussion, including the presence of preclinical RA-related autoantibodies and inflammatory markers, the genetic and environmental factors associated with RA, the models of autoimmune disease development established in
prospective studies of T1DM, and the animal models of disease, it is likely that RA
develops 3 phases, outlined as follows and in Fig. 1A. The initial phase (Phase 1) is
characterized by genetic risk for RA, during which no biomarkers of active autoimmunity and inflammation or symptoms are present. This Phase 1 is followed by environmental and additional genetic influences that lead to a Phase 2 of disease
development—asymptomatic autoimmunity—characterized by the presence of
Preclinical Rheumatoid Arthritis 221
Fig. 1. A model of rheumatoid arthritis (RA) development. (A) Based on RA studies as well as prospective studies in other autoimmune disease (type 1
diabetes mellitus), RA may evolve through 3 phases of disease: Phase 1 5 genetic risk, Phase 2 5 asymptomatic autoimmunity (identified by presence of
autoantibodies) and Phase 3 5 clinically apparent disease. Transition between phases may be caused by interactions between genetic and environmental factors, and/or changes in immune reactivity. (B) RA-related factors that can be measured during the preclinical phases of disease development.
(Adapted from Kolfenbach J, Deane KD, Derber LA, et al. A prospective approach to investigating the natural history of preclinical rheumatoid arthritis
(RA) using first-degree relatives of probands with RA. Arthritis Rheum 2009;61(12):1735–4; with permission.)
222 Deane et al
Fig. 1. (continued)
Preclinical Rheumatoid Arthritis 223
RA-related autoantibodies and other immunologic factors such as T- and B-cell autoreactivity, and perhaps elevated inflammatory markers. Phase 2 may be of variable
length, perhaps influenced by genetic, environmental, or endogenous factors such
as age or gender. As Phases 1 and 2 are asymptomatic, they may collectively be
termed ‘‘preclinical’’ RA. Finally, there is a transition from asymptomatic autoimmunity
to Phase 3, or clinically apparent disease. During this final phase, patients will have
symptoms and signs of active RA, with numerous autoimmune and inflammatory
biomarkers present as well as clear evidence of end-organ damage.
Of note, although in comparison with T1DM the natural history of RA is much less
well understood, there are several studies that have demonstrated results very consistent with this model of disease development for RA. These studies include several
associating the presence of high-risk HLA-DR alleles containing the shared epitope
with RA29,30 and, as described above, the finding of increased levels of autoantibodies
in individuals who later develop RA. In addition, studies in patients with established RA
demonstrating altered synovial pathology in clinically unaffected joints suggest that
there may be a period of time that presymptomatic joint inflammation is present during
RA development.92
PART 3. DEFINING PRECLINICAL RHEUMATOID ARTHRITIS AND TRANSITION
INTO CLINICALLY APPARENT DISEASE
A key aspect of this 3-phase model of RA development is that there is a transition
period from the ‘‘preclinical’’ state (or Phases 1 and 2), where specific disease
markers may be present but there are no symptoms or signs of active inflammatory
disease, to a ‘‘clinical’’ period of RA, when symptoms and signs of active inflammatory
disease are present. There may be agreement that RA-related autoantibody positivity,
in the absence of joint symptoms or other organ injury, in subjects that eventually
develop fully classifiable RA, represents preclinical RA. However, defining this transition from preclinical to clinical disease is more difficult: at what point does clinically
apparent RA begin?
To date, given that the main anatomic site affected by RA is the synovial joint, the
criteria for determining the presence of ‘‘clinically apparent’’ RA have largely focused
on the joints. In the American College of Rheumatology (ACR) 1987 Revised Classification Criteria for RA, 4 of 7 criteria need to be fulfilled for RA to be defined.93
However, it is important to remember that these criteria were developed to help standardize research studies in RA, that all of the disease manifestations that result in
criteria fulfillment take time to develop, and that a patient meeting these criteria
may have truly transitioned from preclinical to clinical RA years prior to fulfilling the
ACR criteria for RA.94,95
In an attempt to investigate early joint disease that may not meet the 1987
Revised ACR Criteria, there are several investigative groups that have sought to
classify inflammatory arthritis (IA) or undifferentiated arthritis (UA) as a distinct clinical entity. Such classification allows for the establishment of prospective clinical
studies to determine the long-term outcomes of patients who present with such
findings, as well as to identify factors that may predict evolution to classifiable
and factors that may indicate that early aggressive therapy to prevent long-term
disability is warranted. Of note, Verweij and colleagues have shown that, in patients
with arthralgia and ACPA positivity but who do not meet classification criteria for RA,
upregulation of certain genes in peripherally-circulating blood cells predicts risk for
future development of fully-classificiable RA (by ACR criteria) within a defined time
period.96
224 Deane et al
The most commonly utilized criteria for IA/UA are the Norfolk criteria and the Leiden
criteria.97–101 The Norfolk criteria define IA as 2 or more swollen joints of duration
greater than 4 weeks.97 In the Leiden criteria, IA/UA is defined as 1 or more joint
with inflammatory findings confirmed by a rheumatologist, with the joint findings not
otherwise classifiable (ie, gout or pseudogout).98 In addition, together the ACR and
the European League Against Rheumatism (EuLAR) are currently developing revised
RA criteria, in part to address the need to link IA to the same long-term prognostic
considerations and need for treatment, as are typical for RA as defined by the earlier
ACR criteria.102
The Norfolk and Leiden criteria for UA/IA, and the new ACR/EuLAR criteria for RA,
may be more useful than the current ACR RA criteria in identifying patients earlier in the
transition from preclinical to clinical RA, and it will be important for studies in preclinical RA going forward to have clearly defined criteria for transition from preclinical
disease in order to understand the evolution of RA, define when in the spectrum of
clinical presentations therapeutic intervention may be necessary, and define a clinical
outcome that is a suitable end point for prevention trials.
PART 4. WHAT CAN WE LEARN BY INVESTIGATING PRECLINICAL RHEUMATOID
ARTHRITIS?
Genetic and Environmental Interactions in Preclinical Rheumatoid Arthritis
As discussed earlier, the genetic and environmental influences that lead to the preclinical phase of disease development are likely key features in the development of RArelated autoimmunity. However, given the observed length of time between the
appearance of autoimmunity and diagnosis of RA, standard case-control study
approaches using subjects with established RA may not optimally allow for the identification of environmental risk factors for RA or at what point the risk factors influence
the development of autoimmunity and disease. For example, as mentioned earlier,
there is now considerable data that supports that gene-environmental interactions
between smoking and specific HLA alleles are associated with ACPA positivity in
established RA.36,56–59,103,104 However, investigating the relationship between these
factors in the preclinical period would help determine whether HLA alleles, smoking,
and ACPA positivity are associated in the absence of synovitis—a finding that would
support a role for smoking as an initial and perhaps causative step in RA-related
autoimmunity.
Inherent in the ‘Phases’ model of RA development discussed above is that there is
a physical location where genetic and environmental factors interact to lead to the
initial RA-related immune dysregulation and break in tolerance. For example, given
the strong association of smoking with RA, and in particular ACPA-positive RA, there
is a theory that initial RA-related immune dysregulation occurs at the mucosal surfaces
of the mouth (periodontal surfaces) or lung, with later spread of RA-related autoimmunity and inflammation to the joints resulting in clinically-apparent synovial
disease.37,39,57,58,105 Real-time prospective study of subjects with RA-related autoimmunity, evidenced by autoantibodies (either prevalent or incident) but no synovitis,
would allow for detailed exploration of mucosal surface immune function. Supporting
this approach, in preliminary work the authors have identified evidence of inflammatory lung injury, including airway and alveolar disease, using high-resolution computed
tomography of the lungs of individuals with RA-related autoantibody positivity but
without joint symptoms or findings, suggesting that RA-related inflammation may
indeed occur initially in the lung.106
Preclinical Rheumatoid Arthritis 225
Evaluation of Autoantibody and Inflammatory Marker Evolution in the Preclinical
Period of Rheumatoid Arthritis Development
There is a growing body of work suggesting that factors involving RA-related autoantibodies including isotype switching, antigen specificity, posttranslational modification and effector function (such as autoantibody glycosylation) may be related to
disease severity and perhaps evolution from UA to RA.107–112 For example, Verpoort
and colleagues111 reported that patients who evolved from UA to RA had a broader
spectrum of ACPA isotypes compared with those with persistent UA at follow-up. In
addition, a study by Ioan-Facsinay and colleagues113 comparing autoantibodies
in North American natives with RA and their healthy FDRs showed ACPA reactivity
in both groups (19% in healthy FDRs vs about 91% in RA cases); however, the fine
specificities of ACPAs differed between RA cases and healthy controls, with reactivity
to citrullinated fibrinogen and vimentin only seen in RA cases. Also in this study, ACPA
isotypes were more limited in healthy FDRs compared with RA cases. As a whole,
these findings suggest that ACPA isotype evolution and specificity may be important
for disease development. As such, investigating the evolution of the isotype changes
and specificity during the preclinical period when the possible transformations from
nonpathogenic to pathogenic states may occur, may lead to key insights into RA
development, and perhaps identification of the ‘‘original sin’’ in RA; that is, the initial
autoantigen that leads to RA-related autoimmunity. In regard to this latter point, based
on the work of several groups, ACPA reactivity to citrullinated a-enolase CEP-1
epitope may indicate that this citrullinated antigen most strongly links exposure to
cigarette smoke and HLA risk alleles in RA.59 If autoimmunity to this citrullinated
antigen could be demonstrated in the preclinical period prior to other autoimmune
responses to citrullinated antigens, the argument that this antigen is the initial one in
RA would be compelling. In addition, prospective evaluation of cytokine/chemokine
type (ie, IL-17, TNFa, or paradigm-specific small molecule profiles) may allow for identification of key inflammatory processes in RA development that may help to identify
the inciting factors for this disease as well as allow us to specifically target aspects of
the immune system for prevention.
Predictive Models for Future Rheumatoid Arthritis
Several prospective and retrospective studies suggest that autoantibodies or combinations of genetic factors and autoantibodies indicate high risk for future RA. In
prospective evaluation (including joint examinations and radiographs of hands and
feet approximately every 2 years) of approximately 2700 Pima and/or Papago Native
Americans in Arizona, USA (a population with an overall prevalence rate of RA of
approximately 5%), followed up to 19 years, del Puente and colleagues1 demonstrated increased risk for incident RA in RF-positive (by sheep cell agglutination) individuals, with the highest risk of 48.3 cases per 1000 person-years seen in those with
a titer of greater than 1:256 at baseline testing. Also in prospective evaluation of 370
FDRs from multicase RA families followed with periodic joint symptom assessment for
a mean of 5 years, Silman and colleagues11 found the overall rate for incident RA to be
approximately 8 per 1000 person-years, with a rate of incident RA in subjects that
were positive for RF at baseline of 34.8 cases per 1000 person-years (calculated
from 4 incident cases of RA out of 24 individuals).
Retrospective biobank studies have also estimated risk for future RA, although
these results are more limited due to lack of prospectively collected data. In their
Swedish biobank study, Rantapaa-Dahlqvist and colleagues7 estimated PPVs for
future RA of 4% if RF-IgM positive alone, 16% if anti-CCP positive alone, and 22%
226 Deane et al
if anti-CCP and RF-IgA positive (these PPV calculations assumed a prevalence of RA
in the general population of 1%). Nielen and colleagues8 estimated a PPV for onset of
classifiable RA within 5 years of 5.9% for subjects that were anti-CCP positive alone,
assuming an incidence rate of RA over 5 years in the general population of 0.001%.
However, this PPV increased to 69.4% if the incidence rate of RA in the population
over 5 years used for calculation was 3.9%. Of note, this higher rate of incident RA
(3.9% vs 0.001%) used by Nielen and colleagues in their PPV calculations was estimated from Silman and colleagues11 1992 study of incident RA in individuals from
multicase RA families, in which a strong family history of RA (R2 members with RA)
may serve as a possible surrogate for additional genetic and/or environmental risk
for RA. Also, in the Nielen study,8 if both RF and anti-CCP were positive, the PPV
for RA diagnosis within 5 years was 100%, regardless of which background incidence
of RA was used for comparison.
Studies that have evaluated risk for future RA have shown that certain genetic
factors, notably HLA alleles containing the ‘‘shared epitope,’’ may increase risk for
future RA.114 However, the ability of genetic factors alone to predict future RA may
be limited, in part due to the high prevalence of these factors in the population—in
North American controls, at least one HLA allele containing the ‘‘shared epitope’’ is
present in about 40% of the population, and PTPN22 risk alleles are present in about
16% of the population.57 As such, prediction of risk for future RA will likely best be
done using combinations of genetic, environmental, and autoantibody factors.
Several studies have already examined the relationship between genetic factors and
autoantibodies in prediction of future RA. Berglin and colleagues,115 using the
Northern Sweden Health and Disease biobank, performed a nested case-control
study to show a strong association between pre-RA diagnosis anti-CCP positivity
and HLA-DRB1*0404 or *0401 alleles and risk for future RA (odds ratio 66.8, 95%
confidence interval [CI] 8.3–539.4). In addition, using data from the same Swedish biobank and similar study design, Johansson and colleagues116 showed a strong association of anti-CCP positivity and 2 copies of the 1858T variant allele of PTPN22 with
future RA (odds ratio 132.0, 95% CI ~18–2721). Studies are also underway to use gene
and environment interactions for prediction of RA, as well as prediction of preclinical
RA-related autoantibody positivity as a surrogate outcome for evolving RA (Elizabeth
Karlson, personal communication, 2009).
There may be other factors that act separately or in concert with genetic and environmental factors to influence transition from asymptomatic to symptomatic RArelated autoimmunity. Majka and colleagues9 and Bos and colleagues17 reported in
their retrospective cohort analyses that subjects with older age at time of diagnosis
of RA had longer duration of preclinical RA-related autoantibody positivity. These findings may be explained by differences in genetic or environmental exposures that vary
by age, or by age-related immune senescence. In addition, these findings suggest that
age or other endogenous factors such as gender may have relevance in predicting
future onset of RA in at-risk populations.
Also, prospective studies of cohorts of patients initially with early symptomatic IA/
UA have allowed for investigation of the effects of genetic and other factors in the
persistence and evolution of symptomatic arthritis. Several Dutch studies have shown
that factors such as age, sex, number of swollen joints, and autoantibody and CRP
status may predict persistent IA at 1 year.98,100,117 In addition, in separate studies,
Feitsma and colleagues118 and van der Helm-van Mil and colleagues119 showed
that the presence of PTPN22 or HLA risk alleles may not significantly increase risk
of transition from UA to RA, but that these genetic risk factors do influence autoantibody presence (HLA) or level (PTPN22). Finally, several preclinical studies including
Preclinical Rheumatoid Arthritis 227
those using the Swedish, Dutch, and NHS biobanks noted an increase in autoantibody
titer and/or inflammatory marker levels in the time period immediately preceding diagnosis.7,8,18,19,21,22 Regarding this latter point, prospective study of biomarker changes
may also be of key interest in understanding the kinetics of preclinical RA and in
predictive models for symptomatic disease.
Although these studies are supportive of the ability of predictive models to determine
risk for future RA, it should be noted that estimates of risk for future RA using stored
samples from biobanks are limited because such studies were not truly prospective.
Of importance is that participants were not subjected to detailed baseline or followup joint examinations, and pre-RA diagnosis samples were assessed retrospectively
in comparison with selected controls after RA had been diagnosed. For these reasons,
the relationship between symptom onset and biomarker positivity is inexact.
Preclinical Prevention of Rheumatoid Arthritis
Several clinical trials have demonstrated that treatment with aggressive therapy in
early RA (that meets 1987 ACR RA criteria) leads to improved clinical outcomes,
and perhaps increased rates of drug-free remission.120,121 As such, currently a major
goal for RA treatment is early identification and treatment of disease.122 In addition,
several investigative groups have evaluated the efficacy of disease-modifying therapy
in individuals who have UA/IA not yet meeting established ACR criteria for RA. For
example, in the Probable Rheumatoid Arthritis Methotrexate versus Placebo Treatment (PROMPT) trial, in patients with UA of duration 2 years or less, use of methotrexate delayed progression to RA as defined by the 1987 ACR criteria, with the
most benefit seen in anti-CCP positive subjects.99 Another small study investigating
abatacept in UA showed a trend toward decreased progression to classifiable
RA.123 Also, several studies utilizing immunomodulation to prevent progression of
T1DM have been performed, and although T1DM has not yet been prevented, studies
have shown that intervention may lead to decreased insulin usage, and decreased risk
for death from ketoacidosis early in disease.124 Finally, in SLE, a retrospective study of
military patients with SLE by James and colleagues125 found that treatment with
hydroxychloroquine in early disease led to decreased progression of SLE-specific
autoantibodies as well as clinical findings. Overall, the results from these studies
suggest that intervention in an even earlier period of RA-related autoimmunity (ie, in
the preclinical period) may lead to prevention of disease.
Unfortunately, as of yet there are no published results of preclinical RA prevention
trials. However, interesting data obtained from database studies suggests that certain
agents such as HMG-CoA reductase inhibitors (statins) that may have some benefit in
treatment of active RA may modify future RA risk.126–128 Jick and colleagues129 have
shown, using a national database in the United Kingdom (N 5 313 RA cases and 1252
controls), a decreased risk for incident RA in patients using statins for hyperlipidemia
(odds ratio 0.59, 95% CI 037–0.96).
Ultimately, these findings and further research may lead to preclinical pharmacologic immunomodulation to prevent disease. Alternatively, perhaps nonpharmacologic tolerization (based on murine models of disease) or risk factor modification in
the preclinical period may be used to abrogate clinically apparent disease; for
example, if a person at high-risk for future RA stopped smoking, this may decrease
the risk for developing clinically apparent arthritis. However, while prevention of RA
is of key importance, implementation of prevention trials will only be possible after
researchers have first developed models in prospective studies to identify accurately
those at high risk for future RA in a definable and relatively short time period necessary
to conduct such studies.
228 Deane et al
PART 5. FUTURE RESEARCH IN PRECLINICAL RHEUMATOID ARTHRITIS
There are multiple approaches to investigate preclinical RA, and these are outlined in
Table 2. The investigation of preclinical RA would ideally take an approach similar to
the Framingham study, which followed a large population over time to investigate
causes of cardiovascular disease using serial measures of biomarkers and clinical
outcomes.130 However, due to the low prevalence of RA, large-scale population
studies at single centers may be impractical due to the cost of screening and relatively
few outcomes of disease. As such, preclinical RA may best be investigated by using
research models similar to those used in studies in T1DM, that is, using a multicenter
approach and prospectively following subjects who are likely to be at higher risk for
RA-related autoimmunity as well as development of clinically apparent disease. One
example of a population at higher risk for RA is FDRs of RA probands, as these
FDRs may have 5- to 7-fold increased risk for incident RA.11 In a multicenter study
in the United States, the authors are currently following prospectively a large cohort
of FDRs of probands with RA (goal N 5 2100).131 To date, a substantial proportion
(~14%, N~1200) of these FDRs exhibit RA-related autoantibody positivity.131 In addition, in Canada, El-Gabalawy and colleagues113,132,133 are currently prospectively
following a cohort of North American Natives who are FDRs of probands with RA,
and have demonstrated intriguing findings regarding differences in ACPA isotypes
and specificities between RA cases and asymptomatic FDRs. These cohorts will be
valuable in investigating the effects of genetic and environmental factors on RArelated autoimmunity, as well as in investigating the evolution of RA-related autoimmunity and inflammation over time. While identification of asymptomatic individuals with
RA-related autoantibody positivity is of interest, these prospective cohort analyses will
also allow for the identification of factors that impact the transition from Phase 1
(genetic risk) to Phase 2 (asymptomatic autoimmunity)—a transition during which
the key early interactions leading to RA-related autoimmunity occur. Examples of
RA-related measures that may be assessed prospectively in preclinical study are
provided in Fig. 1B.
Also, based on the prior success of biobank studies of preclinical RA, additional
samples from yet untapped existing biobanks may be evaluated for RA-related
biomarkers. However, as these retrospective cohorts may lack detailed joint evaluations, the ability to investigate the relationship between immune parameters and
symptomatic disease may be limited.
As an alternative to the prospective or biobank studies discussed earlier, a large
general population could be screened for RA-related genetic traits or RA-related autoantibody positivity to identify those at high risk for disease. From this initial screening,
a smaller group of individuals with high-risk genetic and/or autoantibody markers may
be followed over time to evaluate the evolution of RA-related autoimmunity. For
example, in a health-fair screen of approximately 5000 individuals, the authors have
identified approximately 40 anti-CCP positive subjects without synovitis on examination, and these subjects are now being evaluated prospectively for evolution of
RA-related autoimmunity.134 Such population screening is complicated by cost issues
and the potential for subjects participating in such screening to have existing symptomatic joint disease, thereby missing the ‘‘preclinical’’ window of disease. However,
with appropriate methodologies, population screening may be a reasonable approach
to identify individuals with asymptomatic RA-related autoimmunity.
Of note, given the growing availability of array technologies, it may be possible to
screen large populations at risk of developing a wide variety of autoimmune diseases.
By testing for multiple autoimmune diseases, this approach might also allow for
Preclinical Rheumatoid Arthritis 229
Table 2
Potential methodologies for investigating preclinical rheumatoid arthritis
Study Design Examples Strengths Weaknesses
Retrospective case-control studies
using stored prediagnosis samples
(biobanks):
Finnish, Swedish, and Dutch biobank
studies6–8
United States Military/Department
of Defense Serum Repository9
Nurses’ Health Study18,22
Women’s Health Study22
Biobanks already established and
preclinical samples may be obtained
from cases with known RA
Decreased ability to determine future
risk for disease; unable to ascertain
exact relationship between timing
of appearance of RA-related
biomarkers and symptoms; limited
samples available
Prospective studies:
Populations at high risk for RA
(such as first-degree relatives
of probands with RA, twin studies,
or populations such as Native
Americans with high prevalence
of disease)
Ongoing:
Holers et al131: Studies of the
Etiologies of Rheumatoid Arthritis
(SERA): prospective evaluation of
first-degree relatives of probands
with RA
El-Gabalawy et al113,132,133:
North American Native people in
Central Canada (Cree and Ojibway)
prospectively followed for
evolution of RA-related
autoimmunity. Background
prevalence of RA in population
~2%
Prior:
Native American (Pima and Papago)
studies1
Real-time evaluation of evolution of
RA-related autoimmunity to
determine timing of appearance of
biomarkers in relationship to
environmental exposures and
development of symptomatic
disease; possibility for detailed
assessment of mucosal biology in
preclinical RA
Costly in terms of money and time;
relatively low prevalence of
incident RA and prevalence of
RA-related autoantibodies limits
statistical power
230 Deane et al
Other prospective studies:
Large-scale population screening to
identify individuals with high-risk
features for RA including genetic
factors and RA-related
autoantibody positivity
Health-fair screening in Colorado
identifying anti-CCP positive
asymptomatic individuals who are
recruited for follow-up134
Potentially identifies subjects at risk
for ‘‘sporadic RA’’(as are most cases
in population); may help to
establish prevalence of RA-related
autoantibodies in general
populations
Expensive, and relatively low
prevalence of RA-related
autoantibodies requires large-scale
screening to identify at-risk
individuals
Coupling of prospective RA studies
with other research projects (such
as cardiovascular disease studies)
Multiple studies are likely available Allows for coupling of research
projects perhaps resulting in
decreased costs
Costly in terms of money and effort to
establish screening
Other approaches:
Animal models of disease
Multiple Allows for detailed evaluation of
antigen interactions; may provide
for testing of methodologies for
tolerization
Animal models of arthritis have
substantial differences from human
disease
Population screening for multiple
autoimmune diseases
Multiple Multiple autoimmune diseases may be
studied; array technology for
multiple autoantibody testing
Expensive; optimal diagnostic
accuracy and reproducibility
of testing would need to be
established
Preclinical Rheumatoid Arthritis 231
a more cost-effective way to identify individuals at risk for RA-related autoimmunity as
well as those at risk for other autoimmune diseases that also exhibit preclinical
disease-related autoantibodies, including T1DM and SLE already mentioned, as
well as autoimmune thyroid disease (Graves disease and Hashimoto thyroiditis),
primary biliary cirrhosis, and celiac disease.135,136 With regard to such a strategy, it
is important to understand that in aggregate these diseases affect up to 7% of the
population.135,136 Also, there are data to support the possibility that risk for cardiovascular disease (CVD), the leading cause of death in RA patients, may be increased even
in the preclinical period of RA.137 As such, preclinical evaluation of RA may not only
identify RA-specific factors but also lead to a better understanding of CVD risk in
RA, and perhaps CVD prevention.
In addition to the design and implementation of prospective studies to investigate
the preclinical period of RA development, several other issues regarding research
methodologies in preclinical RA need to be addressed. First, what constitutes positivity for RA-related autoantibodies? At present there are multiple methodologies for
testing RFs and ACPAs, with each kit having different cut-offs for positivity resulting
in a variety of sensitivities and specificities. As such, standardized methodologies
for testing RFs and ACPAs as well as for determining what result is considered positive
will need to be established in order to homogenize testing results and development of
predictive models for future RA. International studies in T1DM have already adopted
standardized autoantibody testing, and these tests are performed in a limited number
of research laboratories to ensure accuracy and reproducibility of testing. Second, as
discussed earlier, we will need to define what constitutes ‘‘preclinical’’ RA as well as
what constitutes transition from asymptomatic RA-related autoimmunity to clinically
apparent disease. Likely this will need standardized symptom and joint count assessments, as well as potentially standardized techniques for imaging of the synovium
using magnetic resonance imaging and/or ultrasound, and standardized synovial
biopsy techniques and tissue processing. Also, it may be useful in preclinical studies
to establish biomarker end points that could be employed in prevention trials. Such
profiles, which may include autoantibodies and inflammatory markers, may be used
as surrogate outcomes for increased risk for future RA. For example, if an asymptomatic individual in a prevention trial has RA-related autoantibodies suggesting high risk
for future RA as well as an elevated CRP suggesting active inflammation, a decrease of
CRP in this individual due to a pharmacologic intervention (in absence of joint symptoms) may be considered a clinically appropriate success in prevention of disease.
This approach is aimed at allowing for a more timely assessment of intervention
success, as joint symptoms may take years to develop. Of note, in terms of symptoms
or examination findings, swollen joints may not be the first indication of transition from
preclinical RA to clinical RA, and perhaps patient-reported measures such as stiffness
or pain in absence of detectable swelling are the first indications of symptomatic RA.
Detailed studies of the preclinical period, closely examining joint symptoms, and
perhaps investigating asymptomatic organ injury using synovial biopsy to discover
asymptomatic synovitis, or joint or lung imaging to detect asymptomatic RA-related
injury, may be necessary to understand truly the evolution from preclinical to clinical
RA. Third, what phenotype of RA will be best to investigate? Will it be best to focus
on seropositive disease, as it will be easier to identify preclinical seropositive RA
due to the presence of specific autoantibodies? Given that seronegative RA may be
distinct from seropositive RA in terms of genetic and environmental risk factors, it
may be worthwhile to focus efforts going forward on seropositive disease.138 Fourth,
to understand the predictive power of RA-related biomarkers for future disease,
relevant control populations for prospective studies of preclinical RA need to be
232 Deane et al
established. This factor is of particular importance when considering that several
preclinical studies in RA have already shown that not all subjects with RA-related autoantibody positivity, including ACPAs, may develop symptomatic RA.4,15 Finally, standardized approaches for assessing epidemiologic exposures that might impact RA
development will need to be established.
In addition to studies in humans, animal models of autoimmune disease may yield
important insights into preclinical autoimmunity. In particular, animal models may be
utilized to understand initial citrullinated protein-specific autoimmunity, or the role of
mucosal surfaces in the generation of autoimmunity. Also, animal models may help
to identify methods to tolerize individuals to citrullinated or other antigens important
to RA in the preclinical period of RA development, a time period in which nonpharmaceutical, immunomodulatory strategies may be more effective prior to the extensive
epitope spreading that has occurred in RA by the time clinical symptoms and signs
of disease appear. Animal studies may also allow the determination of whether novel
treatments focused on the citrullination process itself may be beneficial.
SUMMARY
Based on multiple studies in RA as well as other autoimmune diseases, RA likely
develops in phases exhibited by genetic risk, asymptomatic autoimmunity and, finally,
clinically apparent disease, with transformations between these phases occurring due
to combinations of genetic, environmental, and immunologic factors. Investigating the
preclinical phases of RA development will provide key insights into the factors that
lead to disease, as well as allow for development of predictive models for disease,
and ultimately prevention strategies for RA. Going forward, studies of preclinical RA
may use bio-repositories, but the most effective approach will likely be the use of
prospective cohort studies, with subjects chosen from populations at greater risk
for RA such as FDRs or twin studies, or those identified with high-risk markers for
RA, either genetic or autoantibody, through community screening. In addition to
design and implementation of such prospective studies, the rheumatology community
will need to define with greater clarity what constitutes the transition from preclinical to
clinical RA, as well as standardize autoantibody and inflammatory marker testing.
Although these latter tasks are daunting, investigation of preclinical RA likely gives
us the greatest hope for curing or preventing this disease.
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