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Dual-energy CT gout — SCE Rheumatology MCQ

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HardMusculoskeletal InvestigationsDual-energy CT goutSCE Rheumatology

Synovial fluid from an acutely inflamed knee contains weakly positively birefringent rhomboid crystals. Which crystal is responsible?

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Correct answer: E — Calcium pyrophosphate crystals causing acute CPP arthritis

The best answer is “Calcium pyrophosphate crystals causing acute CPP arthritis”. Rhomboid, weakly positively birefringent crystals identify CPP crystal arthritis. Monosodium urate crystals are needle-shaped and strongly negatively birefringent; basic calcium phosphate is usually not visible with routine polarized microscopy, and the other crystals do not fit the classic morphology.

Reference: EULAR CPPD diagnosis recommendations: https://ard.bmj.com/content/70/4/563