Objectives: To determine the sensitivity and specificity of ultrasonography for gout, and to investigate the relationship with severity of gout.
Methods: In this case-control study, we prospectively enrolled 53 patients with crystal-proven gout and 50 controls. Ultrasonography was performed on 10 joints for each patient (metatarsophalangeal [MTP] joints 1-2, knees, metacarpophalangeal [MCP] joints 2-3) to determine the prevalence of the double contour (DC) sign and tophi in each site.
Results: We assessed 530 joints in gouty patients and 500 in controls. Gouty patients had a mean disease duration 9.2±10.7 years and a mean of 14.7±19.8 acute attacks. Clinical exam revealed tophi in 44% of patients. Mean urate level was 656.7±145.3 μM. Inter-reader agreement between the 2 sonographers was excellent for both DC sign and tophi. The frequency of the DC sign in MTPs, knees and MCPs for gouty patients and controls was 67% vs. 2%, 57% vs. 0%, and 21% vs. 0%, respectively (all p<0.001), whereas that of tophi, only found in gouty patients, was 74%, 42% and 22%, respectively (p<0.001). The sensitivity of the DC sign was 67% for MTPs, 57% for knees and 21% for MCPs, and specificity was high (all >98%). The sensitivity of tophi was 74%, 42% and 22%, respectively, and specificity 100% for all sites. For MTPs, the DC sign, but not tophi, was significantly associated with uricemia (p<0.05) and disease duration (p=0.01).
Conclusions: Ultrasonography has good sensitivity and specificity to diagnose gout. Sensitivity depends on disease duration, joint site and severity of the disease.