Rheumatology: Core Disease Concepts and Clinical Reasoning
Framework for the Rheumatology Section
Approach rheumatology by pattern recognition across four axes: joint distribution (mono/oligo/poly; symmetric vs asymmetric; axial vs peripheral), tempo (acute vs insidious), inflammatory vs mechanical features (morning stiffness >1 hour, improvement with use, nocturnal pain, elevated ESR/CRP favor inflammation), and extra-articular clues (rash, sicca, serositis, renal, pulmonary, ocular).
High-Yield Disease Concepts
Know the classic phenotypes cold: rheumatoid arthritis (symmetric small-joint polyarthritis, prolonged morning stiffness, anti-CCP more specific than RF), SLE (multisystem, ANA sensitive but nonspecific; anti-dsDNA and anti-Sm specific; complement consumption in flares), spondyloarthritis (inflammatory back pain, enthesitis, dactylitis, HLA-B27 association, asymmetric oligoarthritis), crystal disease (gout: negatively birefringent needle-shaped; CPPD: positively birefringent rhomboid, often knee/MCP), polymyalgia rheumatica and giant cell arteritis (age >50, shoulder/hip girdle pain, elevated ESR; ask about headache, jaw claudication, vision), and vasculitis organized by vessel size.
Traps
Questions reward distinguishing sensitivity from specificity (ANA is a screening test, not diagnostic). Watch for mimics: septic arthritis in a monoarticular hot joint is an emergency; do not anchor on gout without arthrocentesis when infection is possible. Drug-induced lupus (hydralazine, procainamide, minocycline) typically spares kidneys and shows anti-histone antibodies. Remember that seronegative does not mean absence of disease, and normal inflammatory markers do not exclude a flare.
Worked Rule of Thumb
For a hot swollen single joint: aspirate before treating. Cell count, Gram stain/culture, and crystals guide the decision. A rule: if the question emphasizes fever, immunosuppression, or a prosthetic joint, prioritize infection until excluded.
Cross-Cutting Integration
Link rheumatologic disease to internal medicine: RA increases cardiovascular and interstitial lung disease risk; SLE affects kidneys and causes cytopenias; gout clusters with metabolic syndrome and CKD. Screen for infection (hepatitis B, latent TB) before biologics, and monitor for treatment complications.