Rheumatoid Arthritis (RA)

01Pathophysiology

Rheumatoid arthritis is a chronic, systemic autoimmune disorder in which the immune system mounts an inappropriate inflammatory attack against the synovial membrane of diarthrodial joints. The disease is initiated when genetically predisposed individuals (particularly those carrying HLA-DR4) encounter an environmental trigger such as cigarette smoke or microbial antigens, which promotes citrullination of self-proteins. Citrullination is a post-translational modification that converts arginine residues to citrulline, creating neoantigens that the immune system recognizes as foreign.

CD4+ T-helper cells are activated and recruit macrophages and B cells into the synovium. Macrophages release pro-inflammatory cytokines, most importantly TNF-alpha, IL-1, and IL-6, which amplify local inflammation and drive systemic features such as fatigue, anemia of chronic disease, and elevated acute-phase reactants. B cells produce rheumatoid factor (an IgM autoantibody directed against the Fc portion of IgG) and anti-citrullinated peptide antibodies (anti-CCP), both of which form immune complexes that deposit in the joint and perpetuate inflammation.

The sustained inflammatory milieu causes the synovial membrane to undergo hyperplasia, transforming into a thickened, invasive tissue called a pannus. The pannus behaves almost like a locally aggressive tissue, eroding into the articular cartilage and subchondral bone. This is why radiographs in established RA show marginal erosions and joint space narrowing. The erosive process is mediated by matrix metalloproteinases (MMPs) and osteoclast activation driven by RANKL signaling from the inflamed synovium.

The reason patients experience morning stiffness lasting more than one hour is directly tied to this pathophysiology. During prolonged rest at night, inflammatory cytokines and edema fluid accumulate in the joint space. Active movement gradually clears these mediators through the lymphatic system, which is why stiffness improves with use. This stands in contrast to osteoarthritis, where stiffness is brief (under 30 minutes) because the mechanism is mechanical friction, not inflammatory accumulation.

Extra-articular manifestations occur because RA is a systemic disease, not merely a joint disease. Rheumatoid nodules (granulomatous lesions on extensor surfaces) reflect the same immune-complex-mediated vasculitis that can affect the lungs (interstitial lung disease, pleuritis), the heart (pericarditis), the eyes (scleritis, keratoconjunctivitis sicca), and the blood vessels (rheumatoid vasculitis). Felty syndrome (RA + splenomegaly + neutropenia) and Caplan syndrome (RA + coal worker's pneumoconiosis with large lung nodules) are classic associations tested in vignettes. Chronic uncontrolled RA can also lead to secondary AA amyloidosis, presenting with nephrotic-range proteinuria.

02Classification and Clinical Manifestation

The 2010 ACR/EULAR classification criteria use a point-based scoring system. A score of 6 or more out of 10 classifies the patient as having RA, provided there is at least one joint with definite clinical synovitis not better explained by another disease.

The clinical manifestations can be organized into articular and extra-articular categories:

03Diagnostic Workup

The best initial serologic test is the combination of RF and anti-CCP ordered together with acute-phase reactants (ESR, CRP). In a classic exam vignette, a middle-aged woman presents with symmetric polyarthritis of the MCP and PIP joints with morning stiffness lasting more than one hour. The next step is to order RF, anti-CCP, ESR/CRP, and X-rays of the hands and feet.

Anti-CCP is the most accurate serologic marker because of its superior specificity (~95%) compared to RF (~85%). RF is sensitive but can be positive in many other conditions (hepatitis C, Sjogren, SLE, infective endocarditis, and even normal aging). A patient who is RF-positive and anti-CCP-positive has a very high probability of RA. However, approximately 15 to 20% of RA patients are "seronegative" (both RF-negative and anti-CCP-negative), so negative serologies do not rule out the disease.

Plain radiographs remain the best initial imaging study and should include both hands and feet (the feet can show erosions even when the hands appear normal). In early disease, X-rays may be normal or show only soft tissue swelling and periarticular osteopenia. As the disease progresses, marginal erosions and uniform joint space narrowing develop. If X-rays are normal but clinical suspicion remains high, MRI or musculoskeletal ultrasound can detect subclinical synovitis and early bone edema.

Synovial fluid analysis is not routinely needed unless the presentation is atypical (acute monoarthritis raising concern for crystal disease or infection). The fluid shows an inflammatory pattern but is critical for excluding gout (needle-shaped, negatively birefringent crystals) and pseudogout (rhomboid-shaped, positively birefringent crystals).

04Management and Treatment

Acute stabilization begins with NSAIDs for pain and low-dose prednisone as a bridge to DMARD therapy. The key concept tested in vignettes is that NSAIDs and glucocorticoids do not prevent joint destruction. They are purely symptomatic. The patient must be started on a DMARD early ("treat-to-target" strategy within 3 months of symptom onset) to prevent irreversible erosive damage.

Methotrexate is the first-line DMARD and the anchor drug for RA. Its mechanism involves inhibition of dihydrofolate reductase and suppression of purine synthesis, resulting in immunosuppression. The dose begins at 7.5 mg once weekly and is titrated up to 25 mg weekly based on response. Patients must receive folic acid 1 mg daily to prevent the most common adverse effects: oral ulcers, nausea, hepatotoxicity, and bone marrow suppression. Monitoring includes a CBC and liver function tests every 4 to 8 weeks initially, then every 8 to 12 weeks once stable.

Critical contraindications for methotrexate include pregnancy (Category X, teratogenic: causes neural tube defects), significant hepatic disease, severe renal impairment (, as MTX is renally cleared), active infection, and significant cytopenias. If methotrexate is contraindicated, leflunomide is the most commonly tested alternative (but leflunomide is also teratogenic). Hydroxychloroquine is the safest DMARD in pregnancy.

Biologic escalation is indicated when methotrexate at adequate doses for 3 to 6 months does not achieve disease remission or low disease activity. TNF-alpha inhibitors are the most commonly used first biologic. Before starting any TNF inhibitor, the patient must be screened for latent tuberculosis (PPD or interferon-gamma release assay) and hepatitis B, because TNF blockade can reactivate both.

Long-term management involves treating to a target of clinical remission or low disease activity, with regular monitoring of disease activity scores, inflammatory markers, and serial imaging to detect new erosions. Glucocorticoids should be tapered and discontinued as soon as the DMARD achieves its effect to avoid complications of chronic steroid use (osteoporosis, diabetes, adrenal suppression).

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most common trap with RA questions involves confusing RA with osteoarthritis based on joint distribution. Test-writers will describe hand pain and stiffness in an older patient to tempt you toward OA, but the key discriminators are the duration of morning stiffness (more than one hour favors RA, less than 30 minutes favors OA), the joints involved (MCP and PIP for RA, DIP and first CMC for OA), and the quality of joint swelling (boggy, warm, soft tissue swelling for RA versus hard, bony enlargement for OA). Never diagnose RA based solely on RF, because RF is positive in many other conditions and even in healthy elderly patients. Anti-CCP is the test that locks in the diagnosis when you need serologic confirmation.

Another common pitfall is the management sequence. A vignette will describe a patient already taking NSAIDs with persistent symptoms, and the question will ask for the "next best step." Students who answer "increase NSAIDs" or "add prednisone" are wrong. The answer is start methotrexate, because the core competency being tested is understanding that DMARDs, not symptomatic therapy, are the foundation of RA treatment. Similarly, if a patient is already on adequate methotrexate and still has active disease, the next step is to add a biologic (TNF inhibitor), not to switch to a different conventional DMARD alone.

Watch for the vignette that presents a woman with RA who is planning pregnancy. Methotrexate and leflunomide are both Category X teratogens. The tested answer is to stop methotrexate, switch to hydroxychloroquine (safe in pregnancy), and ensure the patient has been off methotrexate for at least 1 to 3 months before conception. If a patient on a TNF inhibitor needs TB screening before initiation and the PPD comes back positive, the tested step is to treat latent TB with isoniazid before starting biologic therapy.

Finally, be alert for extra-articular complications used as the clinical hook. A question may describe neck pain and upper extremity weakness in a long-standing RA patient, testing your recognition of atlantoaxial (C1-C2) subluxation, a potentially fatal complication. Another vignette may describe an RA patient with an enlarged spleen and recurrent infections, pointing toward Felty syndrome (RA + splenomegaly + neutropenia). The core competency across all RA questions is the ability to recognize the disease pattern, order the right confirmatory tests, initiate disease-modifying therapy early, and identify dangerous complications.