Imaging tests show potential for early diagnosis of GCA
medwireNews: Findings from two studies presented at the 2018 ACR/ARHP Annual Meeting in Chicago, Illinois, USA, suggest that noninvasive imaging tests may have a role in the detection of giant cell arteritis (GCA).
“For more than 50 years we have gone to temporal artery biopsy as our diagnostic test” for GCA, Anthony Sammel (Royal North Shore Hospital, Sydney, New South Wales, Australia), lead author of the first study, told the press.
He explained that although this is the current gold standard, temporal artery biopsy can give rise to false negative results, and “while it’s a relatively low-risk surgical procedure”, it is “an invasive test”.
Sammel and colleagues investigated the diagnostic accuracy of positron emission tomography/computed tomography (PET/CT) in 58 patients with suspected GCA, all of whom underwent the imaging procedure within 72 hours of starting corticosteroid treatment and prior to biopsy.
Of the 18 patients who tested positive for GCA by PET/CT, 11 had a positive temporal artery biopsy, and three of the seven patients with a negative biopsy result received a subsequent clinical diagnosis of GCA, said Sammel. And of the 40 participants with a negative PET/CT test result, only one had a positive temporal artery biopsy result.
Sammel reported that these findings translated into a sensitivity of 92%, a specificity of 85% and a negative predictive value of 98%, indicating that PET/CT is “a good rule-out test.”
Although he noted that the study was limited by having “modest” patient numbers, Sammel concluded that “we believe this study supports [the use of PET/CT] as a suitable first-line test” for suspected GCA.
In the second study, Berit Dalsgaard Nielsen (Aarhus University Hospital, Denmark) and team evaluated the diagnostic accuracy of another imaging technique, axillary artery ultrasound, for large vessel (LV)-GCA, using PET/CT as a reference.
Talking to medwireNews, Nielsen said: “We know already that ultrasound can diagnose cranial inflammation very well, on the same level or even better than temporal artery biopsy, but for patients who have mainly large vessel inflammation, we have different modalities that can confirm the diagnosis, but we do not know which one is the best.”
The study included 90 patients with suspected LV-GCA, 56 of whom received a confirmed diagnosis based on clinical features and 18F-fluorodeoxyglucose (FDG) PET/CT. The remaining 34 patients did not have the disease, and formed the control group. Ultrasound tests in all patients were carried out by experienced sonographers who were blinded to the PET/CT results.
In all, 36 patients with a diagnosis of LV-GCA had a positive large axillary artery ultrasound result, whereas none of the control individuals had a positive ultrasound, giving sensitivity and specificity values of 78% and 100%, respectively.
Nielsen reported that ultrasound of the temporal arteries gave corresponding sensitivity and specificity values of 73% and 97%, and the sensitivity increased to 91% when large and temporal arteries were analyzed together. She noted that agreement between sonographers was “almost perfect”, at 95% for large vessels and 91% for temporal arteries.
“We think that ultrasound of temporal and axillary arteries can be used as a first-line imaging test in patients suspected of giant cell arteritis, not only those patients with cranial symptoms but also if they are suspected of [having] large vessel involvement”, concluded Nielsen.
When asked which imaging technique – PET/CT or ultrasound – should be used in clinical practice, Nielsen said that “both modalities are good”, and it is “the availability, the price and the skills of sonographers that decide what is the best technique to perform.”
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