Rheumatology — USMLE Step 3 Practice
Rheumatology on USMLE Step 3 covers inflammatory arthritis, connective tissue diseases, crystal arthropathies, and vasculitis. Distinguishing autoimmune conditions by clinical features and serological markers is a core skill.
Frequently Asked Questions
What antibodies are associated with SLE on USMLE Step 3?
ANA is the best screening test (sensitive, not specific). Anti-dsDNA and anti-Sm are specific for SLE. Anti-dsDNA correlates with disease activity (especially nephritis). Anti-Ro (SSA) and anti-La (SSB) are associated with neonatal lupus and secondary Sjogren's. Antiphospholipid antibodies (anticardiolipin, lupus anticoagulant) cause thrombosis and pregnancy loss.
How do you differentiate gout from pseudogout?
Gout: negatively birefringent (yellow when parallel to polarizer) needle-shaped monosodium urate crystals; attacks in first MTP joint (podagra), ankles, knees. Pseudogout: positively birefringent (blue when parallel) rhomboid calcium pyrophosphate crystals; typically affects large joints (knees, wrists). Both treated acutely with NSAIDs, colchicine, or corticosteroids.
What is the Step 3 approach to rheumatoid arthritis treatment?
Start methotrexate early as the anchor DMARD. Add folic acid to reduce side effects. If inadequate response after 3 months, add or switch to biologic (TNF inhibitor: etanercept, adalimumab; or non-TNF: abatacept, tocilizumab). Screen for TB (PPD or IGRA) before starting any biologic.
How do you diagnose and treat giant cell arteritis?
GCA presents in patients over 50 with headache, jaw claudication, scalp tenderness, vision loss, and elevated ESR/CRP. Temporal artery biopsy is the gold standard but start high-dose prednisone (40-60 mg/day) immediately before biopsy results to prevent permanent blindness. If visual symptoms present, give IV methylprednisolone.
What are the systemic complications of ankylosing spondylitis tested on Step 3?
Ankylosing spondylitis (HLA-B27+) complications: uveitis (most common extra-articular manifestation), aortic regurgitation, apical pulmonary fibrosis, IgA nephropathy, and atlantoaxial subluxation. Bamboo spine on X-ray is classic. NSAIDs are first-line; TNF inhibitors for refractory disease.
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