CHICAGO — A combination of PET and CT scanning of the temporal, occipital, maxillary and vertebral arteries — in addition to the chest — demonstrated good diagnostic accuracy for giant cell arteritis compared with temporal artery biopsy, according to data from a late-breaking abstract presented here.
“The clinical challenge we wanted to address in this study is to improve our ability to diagnose this condition. It’s a tricky condition to diagnose, and that is because the presentation often looks like other conditions,” Anthony M. Sammel, MBBS, a rheumatologist at Royal North Shore Hospital in Sydney, said during a press conference. “Someone who comes with these symptoms could very easily have an infection or cancer, and the blood tests we use — the inflammatory markers CRP and sedimentation rate — are often common between these conditions. It is obviously very important that we diagnose [GCA] correctly and diagnose it early because the treatments that we use are inappropriate in other mimicking conditions.”
The study included 64 patients with newly suspected giant cell arteritis who were enrolled over 20 months. All patients underwent PET/CT scanning within 72 hours of beginning corticosteroids or temporal artery biopsy. Results were read by two experienced nuclear medicine physicians who were blinded to the clinical and biopsy data. The reviewers also rated the grade that the tracer uptake exceeded background blood pool for 18 artery segments, as well as the maximum grade per patient (0 = none; 1 = minimal/equivocal; 2 = moderate; and 3 = very marked), according to the abstract.
Fifty-eight patients underwent temporal artery biopsy, 12 of whom (21%) had biopsy-positive GCA. The sensitivity of PET/CT for global assessment of GCA was 92%, and specificity was 85%. Positive predictive value was 61%, and negative predictive value was 98%.
Two out of seven false-positive PET/CT patients experienced disease flares consistent with GCA when corticosteroids were weaned, suggesting the combined scanning modality may have diagnosed GCA more accurately than temporal biopsy.
When an uptake grade cut-off of 1 or more was defined as a positive scan, the sensitivity of PET/CT was 100% with a specificity of 46% compared with temporal artery biopsy. A cut-off of 2 or more resulted in sensitivity and specificity of 83%. Grade 2 or higher uptake localized to the temporal, occipital, maxillary or vertebral arteries occurred among 33% of patients with biopsy-positive disease. According to Sammel, this may have been missed on older-generation scanners.
“PET/CT scan, when we include arteries of the head, neck and chest, has very good diagnostic accuracy for GCA, and we believe the study would support its use as a suitable first-line test for GCA,” Sammel said. “In a significant number of patients, this may mean that they don’t have to go on with temporal artery biopsy.” – by Stacey L. Adams
Sammel reports a relationship with Arthritis Australia, a non-profit organization.
Sammel A. Abstract L15. Presented at ACR/ARHP Annual Meeting, Oct. 20-24, 2018; Chicago.