Acute CPP crystal arthritis — SCE Rheumatology MCQ

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EasyCrystal arthropathiesAcute CPP crystal arthritisSCE Rheumatology

A 38-year-old man has acute painful knee swelling after an intercurrent illness. Examination shows there is a warm effusion without trauma. Investigations show synovial fluid shows rhomboid weakly positively birefringent crystals. The admitting team asks which diagnosis best explains the whole presentation. What is the most likely diagnosis?

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Correct answer: D — Acute CPP crystal arthritis

Acute CPP crystal arthritis is the best answer because the pattern described is most consistent with Acute CPP crystal arthritis, including the distribution of symptoms and the targeted investigation results. Osteoarthritis flare is a plausible distractor, but it does not account for the key discriminator in the stem. Leflunomide hepatotoxicity and Basic calcium phosphate disease would be more appropriate in a different clinical pattern or at another point in the pathway, while Reactive arthritis is suboptimal for this presentation. Clinical pearl: in SCE-style questions, the decisive clue is usually the pattern across joints, extra-articular features and targeted immunology rather than a single antibody result.

Reference: NICE NG219; BSR hot swollen joint guideline; EULAR crystal arthropathy recommendations