When any one feature was considered a positive ultrasound for gout, sensitivity was 76.9%, specificity was 84.3%, PPV was 83.3%, and NPV was 78.2%.
Comparing early to late disease, the researchers found no significant difference in sensitivity or specificity. Subjects with tophi on clinical examination had higher sensitivity and PPV compared with those without clinically detected tophi, while specificity and NPV were lower.
“Early gout didn’t look that different from late gout,” says Dr. Ogdie.
Subjects with an actively tender or swollen first MTP joint and those with elevated serum urate levels had lower specificity and NPV for all ultrasound features.
The researchers also found that a positive ultrasound finding for gout was associated with suspected tophi upon examination, higher serum urate level and abnormal radiographic findings, which means that ultrasound may not be necessary to diagnose gout in these patients, but it can still be helpful in patients without obvious gout upon examination.
Conclusions
In general, “The specificity is high,” Dr. Ogdie says, “so we can be fairly confident that a positive ultrasound is suggestive of gout. If it’s negative, we could still be missing people who do have gout.”
In previous studies, gout has been shown to be difficult to discern from calcium pyrophosphate deposition disease (CPDD) by ultrasound, so the study team examined the specificity of ultrasound features for gout among patients with CPDD (confirmed by aspirates). They found sensitivity and PPV were still high for gout.
“Ultrasound is a pretty good test for gout,” Dr. Ogdie says. “Just be aware that it could miss people with gout who have a negative test.”
Kelly April Tyrrell writes about health, science and health policy. She lives in Madison, Wis.
Reference
- Ogdie A, Taylor WJ, Neogi T, et al. Performance of ultrasound in the diagnosis of gout in a multicenter study comparison with monosodium urate monohydrate crystal analysis as the gold standard. Arthritis Rheumatol. 2017 Feb;69(2):429–438.
