Pseudogout (CPPD) — RACP Adult Medicine MCQ

Instant feedback + full explanation. One question, done properly.

EasyRheumatologyPseudogout (CPPD)RACP Adult Medicine

A 28-year-old man presents with acute monoarthritis of the right knee. Joint aspiration yields turbid fluid with positively birefringent rhomboidal crystals. His serum urate is 0.28 mmol/L. What is the diagnosis?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: E — Pseudogout (calcium pyrophosphate deposition disease)

Positively birefringent, rhomboidal (brick-shaped) crystals under compensated polarised light microscopy are diagnostic of calcium pyrophosphate deposition (CPPD) disease ('pseudogout'). Negatively birefringent, needle-shaped crystals indicate gout. The normal serum urate helps exclude gout (though urate can be normal during an acute gout flare). CPPD is associated with hyperparathyroidism, haemochromatosis, hypomagnesaemia, and hypothyroidism – these should be screened for.

Reference: eTG – 2025 – Rheumatology