To examine the accuracy of dual-energy computed tomography (DECT) vs ultrasound or their combination for the diagnosis of gout.

Using prospectively collected data from an outpatient rheumatology clinic at a tertiary-care hospital, we examined the diagnostic accuracy of either modality alone or their combination, by anatomical site (feet/ankles and/or knees), for the diagnosis of gout. We used two standards: (1) demonstration of monosodium urate crystals in synovial fluid (gold), and (2) modified (excluding DECT and ultrasound) 2015 ACR-EULAR gout classification criteria (silver).

Of the 147 patients who provided data, 48 (33%) had synovial fluid analysis performed (38 were MSU-crystal positive) and mean symptom duration was 9.2 years. 100 (68%) patients met the silver standard. Compared with the gold standard, diagnostic accuracy statistics for feet/ankles DECT, feet/ankles US, knees DECT, and knees ultrasound were: sensitivity, 87%, 84%, 91%, 58%; specificity, 100%, 60%, 87%, 80%; PPV, 100%, 89%, 97%, 92%; NPV, 67%, 50%, 70%, 33%; AUC, 0.93, 0.72, 0.89, 0.66. Combining feet/ankles DECT with ultrasound or knees DECT with ultrasound led to a numerically higher sensitivity compared with DECT alone, but overall accuracy was lower. Similarly, combining imaging knees to feet/ankles also yielded a numerically higher sensitivity and NPV compared with feet/ankles DECT alone, without differences in overall accuracy. Findings were replicated compared with the silver standard, but with lower numbers.

Feet/ankles or knees DECT alone had the best overall accuracy for gout diagnosis. DECT/US combination or multiple joint imaging offered no additional increase in overall diagnostic accuracy.