Rheumatology and Immunology
Core concepts
Understand the approach to joint pain: inflammatory versus mechanical, monoarticular versus polyarticular, and the urgency of septic arthritis (joint aspiration before antibiotics). Know the classification and features of rheumatoid arthritis (symmetrical small-joint, anti-CCP, extra-articular), spondyloarthropathies, crystal arthritis (gout, pseudogout), and connective tissue diseases (SLE, Sjögren's, scleroderma). Be familiar with vasculitis syndromes and their organ involvement, and the basics of immunotherapy and biologic safety (screening for TB and hepatitis before anti-TNF).
Traps
Questions test septic arthritis versus gout - both cause a hot swollen joint; aspirate for crystals and culture. Do not miss drug-induced lupus (anti-histone antibodies) or antiphospholipid syndrome (thrombosis, pregnancy loss, prolonged APTT). Remember that a normal uric acid does not exclude acute gout. In SLE, monitor for lupus nephritis with urinalysis and complement levels.
Rule of thumb
Any hot, swollen joint with fever: aspirate before antibiotics unless the patient is septic and unstable, in which case treat and aspirate as soon as possible.
Worked example
A young woman with malar rash, arthralgia, and proteinuria: check ANA, anti-dsDNA, complement, and urinalysis; a falling complement with rising dsDNA suggests active lupus nephritis requiring nephrology input.