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DECT Specificity in Gout — SCE Rheumatology MCQ

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ModerateMusculoskeletal ImagingDECT Specificity in GoutSCE Rheumatology

A 60-year-old man has recurrent episodes of acute first metatarsophalangeal joint arthritis, but joint aspiration is not feasible. Dual-energy CT shows colour-coded deposits consistent with monosodium urate at the first metatarsophalangeal joint and within the Achilles tendon. Which statement best describes the diagnostic performance of dual-energy CT in gout?

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Correct answer: C — Specificity is about 90%, but sensitivity falls in recent-onset, low-burden gout.

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

D is correct. DECT distinguishes material composition using attenuation at two X-ray energy levels and can display monosodium urate deposition within joints, tendons and other periarticular tissues. A meta-analysis found person-level specificity of approximately 91% and sensitivity of 81%. Diagnostic sensitivity is substantially lower in recent-onset gout or when the crystal burden is small; at disease duration of 6 weeks or less, pooled joint-level sensitivity was only 55%. Thus, a negative scan does not exclude early gout. DECT is not restricted to clinically apparent tophi and is principally used to identify urate rather than CPP deposits. Specificity is high but not perfect because artefacts and some degenerative changes can generate false-positive colour coding. NICE accepts DECT when aspiration is impracticable or diagnostic uncertainty persists.

Reference: Gamala M, Jacobs JWG, van Laar JM. The diagnostic performance of dual energy CT for diagnosing gout: a systematic literature review and meta-analysis. Rheumatology (Oxford). 2019;58:2117–2121. https://pubmed.ncbi.nlm.nih.gov/31089688/