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Negative Crystal Analysis — SCE Rheumatology MCQ

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ModerateCrystal ArthropathyNegative Crystal AnalysisSCE Rheumatology

A 50-year-old man has recurrent attacks of abrupt-onset severe pain, erythema and swelling of the first metatarsophalangeal joint, with complete resolution between attacks. His serum urate measured between attacks is 510 micromol/L. During the latest flare, synovial fluid is inflammatory, but no monosodium urate crystals are identified on a single examination by compensated polarised light microscopy; Gram stain and culture are negative. Which is the most appropriate interpretation of the negative crystal analysis?

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Correct answer: B — A single negative crystal examination does not exclude gout; the clinical features should be integrated and ultrasound or dual-energy CT considered if uncertainty remains

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

Option C is correct. Demonstration of negatively birefringent monosodium urate crystals establishes a definite diagnosis, but a single negative synovial-fluid examination does not exclude gout. False-negative results may occur because of sampling, low crystal burden or observer-dependent detection. This patient has a strongly supportive phenotype: recurrent, rapidly developing podagra with complete intercritical resolution and persistent hyperuricaemia. NICE recommends further assessment when the diagnosis remains uncertain, including ultrasound or dual-energy CT where appropriate. Repeat expert microscopy may also be considered when clinically justified, but it is not mandatory during the same flare, so A is too absolute. B and D incorrectly treat microscopy as perfectly sensitive. E is also incorrect because DECT is supportive rather than the only remaining route to diagnosis and has limited UK availability.

Reference: National Institute for Health and Care Excellence. Gout: diagnosis and management (NG219), recommendations 1.1.8–1.1.9. 2022. https://www.nice.org.uk/guidance/ng219/chapter/Recommendations