CPPD — SCE Rheumatology MCQ

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EasyCrystal ArthropathiesCPPDSCE Rheumatology

A 78-year-old woman develops acute painful swelling of the knee 2 days after admission with pneumonia. Radiograph shows chondrocalcinosis of the menisci. Synovial fluid contains weakly positively birefringent rhomboid crystals and culture is negative. What is the most likely diagnosis?

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Correct answer: A — Acute calcium pyrophosphate crystal arthritis

Explanation lettering: E = shown as A · D = shown as B · B = shown as D · A = shown as E

Acute calcium pyrophosphate crystal arthritis is best because rhomboid weakly positively birefringent crystals and chondrocalcinosis indicate acute CPP crystal arthritis. A is less suitable because septic arthritis is less likely with negative culture but must be excluded; B is less suitable because OA flare alone does not explain crystals and intense synovitis; C is less suitable because gout crystals are needle-shaped and negatively birefringent; D is less suitable because RA does not cause acute crystal-positive monoarthritis. Clinical pearl: intercurrent illness can precipitate pseudogout in older inpatients.

Reference: BSR gout guideline; Oxford Textbook of Rheumatology