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Acute CPPD Knee — RACP Adult Medicine MCQ

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EasyRheumatologyAcute CPPD KneeRACP Adult Medicine

A 80-year-old woman with a history of OA presents with an acutely swollen right knee. She is afebrile. WCC is normal. Joint aspirate: WCC 18000 (70% PMNs), weakly positively birefringent rhomboid crystals. X-ray shows chondrocalcinosis of the menisci. What is the most likely diagnosis?

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Correct answer: D — Calcium pyrophosphate disease

Acute knee monoarthritis in an elderly woman with chondrocalcinosis on X-ray and positively birefringent rhomboid crystals is acute CPPD arthritis (pseudogout). CPPD arthritis commonly affects the knee (unlike gout which prefers the 1st MTP). Associated with: age, haemochromatosis, hyperparathyroidism, hypomagnesaemia, and hypothyroidism. Screen for metabolic causes in patients <60.

Reference: eTG Rheumatology – 2024 – CPPD; EULAR 2024