Rheumatology and Clinical Immunology
The rheumatology block asks you to recognise a pattern, interpret autoantibodies in context, and act immediately when an organ is threatened.
ANCA-associated vasculitis
c-ANCA/anti-PR3 points to granulomatosis with polyangiitis (upper airway, lung, kidney); p-ANCA/anti-MPO suggests microscopic polyangiitis or eosinophilic granulomatosis with polyangiitis. Induction is high-dose glucocorticoids plus rituximab or cyclophosphamide; plasma exchange is reserved for diffuse alveolar haemorrhage or anti-GBM disease.
Systemic lupus erythematosus
Diagnosis combines clinical and immunologic criteria. Anti-dsDNA and anti-Sm are specific, and complement falls with activity. Hydroxychloroquine is advised for all patients; nephritis is treated with mycophenolate or cyclophosphamide.
Crystal arthritis
Definitive diagnosis means negatively birefringent needle-shaped crystals. Acute treatment is an NSAID, colchicine, or glucocorticoid. Do not stop urate-lowering therapy during a flare; start it with prophylaxis and titrate urate below 6 mg/dL.
Giant cell arteritis
Age over 50, new headache, jaw claudication, visual symptoms, elevated ESR. Give glucocorticoids immediately and arrange temporal artery biopsy within two weeks; biopsy remains informative after steroids have started.
Worked example
A 68-year-old reports a new temporal headache with jaw claudication and ESR 80 mm/h. Give prednisone 60 mg immediately (IV methylprednisolone if vision is threatened) and then biopsy. Reasoning: steroid pretreatment prevents blindness and does not invalidate the biopsy for up to two weeks, so waiting for histology is the wrong order of operations.
Traps that cost marks
- Using ANA as a screening test for nonspecific pain; it is positive in a large fraction of healthy people.
- Repeating that a febrile patient with rash and arthritis "must be infected" while missing adult Still disease.
- Withholding steroids in suspected giant cell arteritis pending biopsy.