Rheumatology and Musculoskeletal Medicine
Inflammatory arthritis
Rheumatoid arthritis is symmetrical, affects small joints and causes morning stiffness over an hour; anti-CCP is more specific than rheumatoid factor. Start methotrexate early with folic acid cover, checking baseline bloods, renal and liver function, and hepatitis serology. Avoid methotrexate in pregnancy and in significant liver disease.
Connective tissue disease and vasculitis
ANA is sensitive but not specific; anti-dsDNA and complement track lupus activity, and lupus nephritis requires biopsy. In ANCA-associated vasculitis, c-ANCA/anti-PR3 suggests granulomatosis with polyangiitis and p-ANCA/anti-MPO suggests microscopic polyangiitis or eosinophilic granulomatosis; send urine for every suspected case.
Giant cell arteritis and polymyalgia
Any patient over 50 with a new headache, jaw claudication or visual symptoms and a raised ESR needs immediate high-dose corticosteroids - never wait for temporal artery biopsy, because vision lost is lost permanently.
Crystal arthritis and the hot joint
Gout crystals are needle-shaped and negatively birefringent; pseudogout crystals are rhomboid and positively birefringent. Aspirate a hot joint before antibiotics if at all possible, and consider septic arthritis whenever there is fever or a prosthetic joint.
Traps: interpreting a positive ANA as diagnostic of lupus; giving allopurinol without cover during a flare; missing cauda equina syndrome in back pain with saddle anaesthesia and urinary retention.
Rule of thumb: in an older patient with a new unilateral headache plus a raised ESR or CRP, start steroids the same day and investigate afterwards.