Gout Crystal Arthritis — RACP Adult Medicine MCQ

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EasyRheumatologyGout Crystal ArthritisRACP Adult Medicine

A 65-year-old man presents with an acutely swollen hot knee. Joint aspirate: WCC 45000 cells/μL (90% PMNs), negatively birefringent needle-shaped crystals under polarised microscopy. Gram stain negative. What is the most likely diagnosis?

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Correct answer: C — Gout (monosodium urate)

Inflammatory synovial fluid (WCC >2000, predominantly PMNs) with negatively birefringent needle-shaped crystals is acute gout (MSU crystal arthritis). Negative birefringence = yellow when parallel to the compensator. Gram stain/culture should always be sent even when crystals are found (gout and septic arthritis can coexist in ~5%). Treatment: colchicine, NSAIDs, or prednisolone.

Reference: eTG Rheumatology – 2024 – Crystal Arthropathy; ARA 2024