PET/CT has good accuracy for diagnosing GCA



– Combined PET/CT has good diagnostic accuracy, including a 98% negative predictive value, when compared with temporal artery biopsy for suspected giant cell arteritis, according to findings from a study of 64 patients.

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Study participants included patients with newly suspected giant cell arteritis (GCA) and all underwent PET/CT from the vertex to the diaphragm within 72 hours of starting corticosteroid therapy and prior to undergoing temporal artery biopsy (TAB). Two nuclear medicine physicians blinded to clinical and biopsy data identified GCA in the scans of 12 of 58 patients (21%) who ultimately underwent both PET/CT and TAB, Anthony M. Sammel, MBBS, reported at the annual meeting of the American College of Rheumatology.

Compared with TAB, which is the standard of care for diagnosing GCA in most centers, global GCA assessment by PET/CT had a sensitivity of 92%, specificity of 85%, and positive predictive value of 61%, said Dr. Sammel, a rheumatologist at Royal North Shore Hospital in Sydney.

The findings, and particularly the 98% negative predictive value, suggest that PET/CT could be used first line to rule out suspected GCA, although the sample size in the study was modest, he noted.

“I believe [the findings] would support PET/CT, when we include the head, neck, and chest, as a first-line test for patients newly suspected of having giant cell arteritis. I think we do need to be mindful that it’s not perfect,” he said, explaining that a TAB is warranted in a patient with a negative scan despite a clinician’s sense that there is a high likelihood of GCA.

However, the findings suggest that a negative study in a low to moderate risk patient would be “very, very reassuring,” and as such patients probably do not need a biopsy, he said in a video interview in which he also discussed cost-benefit issues with respect to PET/CT in this setting.

Of note, PET/CT diagnosed alternative conditions, including cancer and infections, that can mimic GCA in 13 study participants. At least one of those patients “may well have come to serious harm” on immunosuppressive therapy had his cervical spine infection gone undiagnosed, he said.

This study was funded by Arthritis Australia. Dr. Sammel reported having no relevant disclosures.

SOURCE: Sammel AM et al. ACR Annual Meeting, Abstract L15.

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