MELBOURNE, Australia — PET/CT scanning should be considered as an alternative to Doppler ultrasound in the diagnosis of cranial giant cell arteritis (GCA), as technological advances mean the imaging technique now has much greater resolution and accuracy for cranial arteries, according to data presented at the 22nd International Vasculitis Workshop (IVW) 2026.

An international prospective cross-sectional study compared the diagnostic accuracy of digital FDG PET/CT with Doppler ultrasound in 84 adults whose symptoms and levels of inflammatory markers suggested GCA.

Aubert Roy, MD, nuclear radiologist of McGill University and Jewish General Hospital in Montréal, Canada, told the conference that diagnosis and subclassification of GCA were challenging, particularly when it affected not only the large vessels such as the aorta but also the slightly smaller vessels in the brain.

The current gold standard for diagnosis is to use Doppler ultrasound or biopsy, although increasingly FDG PET/CT is used for the diagnosis of large-vessel GCA, which affects large vessels in the trunk and the brain.

However, Roy told Medscape Medical News that both ultrasound and biopsy had limitations when it came to evaluating cranial involvement, and there was a risk of false-negative results. “Whereas [with] PET scan, it’s more standardized, and it can assess the whole body,” he said.

Technological improvements such as the development of digital FDG PET/CT have also significantly increased its spatial resolution, providing much crisper imaging, particularly of the cranial arteries.

That prompted a study to look at whether the role of FDG PET/CT in the diagnosis of large-vessel GCA could be expanded to include patients with cranial symptoms as a way to examine the involvement of the smaller cranial arteries.

The study ran in five centers across Canada, France, and the Netherlands, from 2018 to 2024. Patients were evaluated with both FDG PET/CT and Doppler ultrasound, with optional biopsy, and the results were independently interpreted by two blinded readers, with the primary endpoint being diagnosis at 6 months.

Of the 84 patients, 44 were diagnosed with GCA; 16 were subclassified as having isolated cranial GCA, six had GCA with only large-vessel involvement, and 16 were a mix of both. Six patients could not be subclassified due to false-negative results on the scan.

Roy drew the audience’s attention to the 16 patients with only cranial vessel involvement. “Because the role of PET scan was traditionally more limited to the large vessels, these are 16 patients where we would have completely missed the diagnosis if we did not look at those smaller cranial arteries, because the only vessels that had visible inflammation on the PET scan were from the neck up,” he said.

He used the example of a 70-year-old woman who presented with a headache and high levels of C-reactive protein and was suspected of having GCA. FDG PET/CT showed increased uptake of FDG in the cranial arteries, but no abnormal uptake in the large vessels below the neck.

Corticosteroids’ Influence on PET/CT

A question was asked about what influence corticosteroid use would have on PET/CT scans. The study excluded patients who had been on corticosteroids for more than 3 days before the scan, with Roy explaining that the steroid use would affect the uptake of FDG.

“We therefore showed in our study that FDG PET/CT scans showed a high diagnostic performance, especially when we incorporate cranial artery assessment,” Roy told the conference. There was also high concordance between the two independent observers, and Bayesian analysis suggested the FDG PET/CT may even be more sensitive than ultrasound.

Commenting on the presentation, Sebastian Unizony, MD, from Massachusetts General Hospital and Harvard Medical School in Boston, told Medscape Medical News the data showed that PET/CT was able to pick up patients who were taking up the FDG only in the cranial arteries. “What it says is that if you do a PET/CT from the head down, you have more chances to make a diagnosis than if you do an ultrasound,” he said.

However, he also noted the challenges of trying to get an FDG PET/CT within 3 days of a patient starting corticosteroids.

Roy did address that issue in his presentation, commenting that it was important not to delay the onset of corticosteroid treatment for a PET/CT scan. “When we go to nuclear medicine conferences, we try to do a lot of advocacy for centers to open up emergency spots in their department for urgent scans such as infection and inflammation,” he said. “Because if there’s a clinical suspicion of GCA, of course we don’t want to delay the onset of treatment.”

The study was supported by a Canadian Rheumatology Association Foundation grant. No conflicts of interest were declared.