Background/Purpose: Giant Cell Arteritis (GCA) poses diagnostic challenges for clinicians as there is no universal gold standard. We hypothesize that launching a Fast-Track Ultrasound (US) clinic by rheumatologists may spare the need for a biopsy. Therefore, we aimed to assess the diagnostic performance of temporal artery (TA) US in this setting.

Methods: In this Canadian monocentric retrospective cross-sectional analysis, 106 subjects were identified from the Fast-Track clinic between 05/2020-05/2022 (99 after exclusion). Each subject had an US of the temporal and axillary arteries according to a standardized protocol for either suspicion of new-onset or relapse of GCA. The pretest probability was calculated using the Southend probability score (high, medium or low). The sensitivity (Sn), specificity (Sp), positive predictive value (PPV) and negative predictive value (NPV) were calculated using the rheumatologist final diagnosis as the gold standard.

Results: TA US demonstrated a sensitivity of 80.0% [95% confidence interval (CI) 59.3; 93.2% ], a specificity of 91.7% (95% CI 83.2; 97.0%), a PPV of 76.9% (95% CI 60.2; 88.0%), and a NPV of 93.2% (95% CI 86.1; 96.7%). 30, 44, 29 subjects were at high, medium, and low risk, respectively. Of those subgroups, subjects at high risk had higher PPV with a lower NPV, while similar Sn/Sp were observed between all three subgroups (see Table).

Conclusion: Our findings confirm the validity of TA US as a diagnostic tool for GCA and highlight the importance of Fast-Track US clinics. Future studies will inform on the role of TA biopsy in the setting of increasing use of US.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/diagnostic-performance-of-a-newly-launched-canadian-fast-track-ultrasound-clinic-performed-by-rheumatologists-for-diagnosis-of-giant-cell-arteritis/