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Synovial fluid CPP crystals — SCE Rheumatology MCQ

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ModerateMusculoskeletal InvestigationsSynovial fluid CPP crystalsSCE Rheumatology

A 53-year-old woman has acute wrist swelling and synovial fluid rhomboid weakly positively birefringent crystals with negative culture. What is the most likely diagnosis?

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Correct answer: C — Calcium pyrophosphate crystal arthritis

Calcium pyrophosphate crystal arthritis is the single best answer because rhomboid positively birefringent crystals identify CPP crystal arthritis. The stem is testing diagnostic synthesis, not isolated recall, so the relevant clinical pattern and risk context determine the answer. Rheumatoid arthritis is less suitable because it fits a different clinical pattern or a different treatment threshold; Systemic lupus erythematosus, Psoriatic arthritis and Gout do not address the key discriminator in this vignette. Clinical pearl: in SCE-style rheumatology questions, autoantibodies, imaging and synovial fluid findings should be interpreted with the whole phenotype.

Reference: BSR hot swollen joint guidance; EULAR imaging/autoantibody recommendations