Performance characteristics and predictors of temporal artery ultrasound for the diagnosis of giant cell arteritis in routine clinical practice in a prospective cohort.

Objective. The diagnosis of giant cell arteritis (GCA) is primarily a clinical one. Temporal artery (TA) ultrasound (US) has been proposed as a new diagnostic tool. We aimed to assess the performance characteristics of TA US in routine clinical practice. Methods. All patients presenting with suspected GCA to our institution are recruited to a prospective registry. Patients who had both a TA US and biopsy (TAB) performed at the time of presentation were included in the current study. The performance characteristics of TA US was compared to physician diagnosis at six months following presentation. Predictive factors for a positive TA US were explored in univariate and multivariable logistic regression analyses. Results. 162 patients were included, 123 (76%) with GCA. Mean (SD) duration of glucocorticoid therapy was 6.6 days (19.4) at the time of TA US. TA US had a sensitivity of 52.8% (95% CI 43.7, 61.9) and specificity of 71.8% (95% CI 54.9, 84.5) for the diagnosis of GCA. Glucocorticoid duration did not significantly impact the results. A sequential strategy of TA US followed by TAB in the case of a negative US had a sensitivity of 78.9% (95% CI 70.1, 85.5) and specificity of 71.8% (95% CI 54.9, 84.5), equivalent to a simultaneous testing strategy. The only factor independently predictive of a positive TA US was male sex (OR 5.53, 95% CI 2.72 to 11.22, p<0.001). Conclusion. TA US is potentially useful in the diagnosis of GCA; however, interpretation of its results requires knowledge of the performance characteristics in the target population.