Rheumatology and Immunology
This domain tests pattern recognition in inflammatory arthritis, crystal disease, connective tissue disease and vasculitis, with emphasis on what to do before starting immunosuppression.
Approach
Decide first whether the process is inflammatory or mechanical, then whether it is monoarticular, oligoarticular or polyarticular, then look for extra-articular features.
Rheumatoid arthritis
Diagnosis uses the ACR/EULAR 2010 criteria - joint involvement, serology, acute-phase reactants and symptom duration. Methotrexate is first-line disease-modifying therapy. Before any biologic, screen for latent tuberculosis and hepatitis B, and update vaccinations.
Crystal arthritis
Gout crystals are needle-shaped and negatively birefringent; pseudogout crystals are rhomboid and positively birefringent. Do not stop established allopurinol during a flare; when starting urate-lowering therapy, cover with prophylaxis.
Connective tissue disease
ANA is sensitive but not specific. Anti-dsDNA and anti-Sm are specific for SLE; complement falls during active disease.
Vasculitis and giant cell arteritis
Giant cell arteritis affects those over 50 with headache, jaw claudication and raised ESR; give steroids immediately and arrange biopsy within two weeks, never waiting for biopsy to treat. c-ANCA with anti-PR3 suggests granulomatosis with polyangiitis; p-ANCA with anti-MPO suggests microscopic polyangiitis.
Worked example
An acutely hot knee aspirate shows needle-shaped negatively birefringent crystals. This is gout: treat the flare with an NSAID, colchicine or steroid, and discuss urate-lowering therapy with prophylaxis rather than starting it unopposed.
Traps that cost marks
- Stopping allopurinol during a flare.
- Waiting for temporal artery biopsy before giving steroids.
- Starting a TNF inhibitor without TB and hepatitis B screening.