PET Scan at Diagnosis May Help to Predict Aneurysm Risk in Patients With Giant Cell Arteritis

Lucy Hicks

October 02, 2023

PET scans may serve as both a diagnostic and prognostic tool in giant cell arteritis (GCA), according to a new study.

In over 100 patients with GCA who underwent 18F-fluorodeoxyglucose (FDG) PET imaging, those with elevated FDG uptake at diagnosis were more likely to develop thoracic aortic aneurysms.

"PET-CT has an excellent diagnostic accuracy for the diagnosis of GCA, certainly if both extracranial and intracranial vessels were assessed. This study shows that performing PET imaging at diagnosis in patients with GCA may also help estimate the future risk for aortic aneurysm formation," wrote lead author Lien Moreel, MD, of the department of internal medicine at University Hospitals Leuven, Belgium, in an email to Medscape Medical News. "PET imaging at diagnosis can provide both diagnostic and prognostic information in one imaging tool in patients with GCA."

Previous retrospective studies have found an association between FDG uptake at diagnosis and risk for aortic complications, but "prospective studies confirming these findings are lacking," the investigators write. The study was published online today in Annals of Internal Medicine.

In the study, Moreel and colleagues prospectively followed 106 individuals diagnosed with GCA who received FDG-PET within 3 days after starting glucocorticoids. Patients also had CT imaging at diagnosis and then CT imaging annually for up to 10 years. 

A PET scan was considered positive with an FDG uptake of grade 2 or higher in any of seven vascular regions (thoracic and abdominal aorta, subclavian, axillary, carotid, iliac, and femoral arteries). Researchers also used the results to quantify a total vascular score (TVS). Out of the entire cohort, 75 patients had a positive PET scan result.

These patients had a larger increase in the diameter of the ascending aorta and the descending aorta, as well the volume of thoracic aorta after 5 years, compared with those who had a negative PET scan result. These changes were also associated with higher TVS at diagnosis. Of the 23 patients who developed an aortic aneurysm, 18 had a positive PET scan at diagnosis.

The risk of incident thoracic aortic aneurysms was calculated to be 10 times higher in patients with positive PET scans. Fourteen of the 15 patients (93%) with an incident thoracic aortic aneurysm had positive PET results.

Dr Kenneth Warrington

Up to now, "we've had no way of predicting which patients might be at risk of this potentially serious complication," Kenneth Warrington, MD, chair of the department of rheumatology and director of the Vasculitis Clinic at the Mayo Clinic in Rochester, Minnesota, told Medscape. He was not involved with the research.

He hopes that the findings will help inform clinicians on how patients with GCA should be evaluated and monitored. Although the American College of Rheumatology conditionally recommends non-invasive imaging in patients newly diagnosed with GCA, guidance for follow-up on these patients is less clear, he said.

"There are no clear guidelines, but most clinicians who take care of patients with GCA do obtain imaging periodically," he said. "There is a lot of variability in the practice in terms of which type of scan is used and how often it's done."

Although this study did not specifically look at the benefit of screening patients, "we think that follow-up of aortic dimensions seems to be warranted in GCA patients with a positive PET scan result, especially in those with high intensity and broad extent of vascular inflammation," Moreel said. "However, the added value of screening and the interval required should be addressed in future studies."

Applying this study's protocol in practice in the United States might be difficult, Warrington noted, as it can be challenging logistically to get imaging done within 3 days of starting steroids. However, Moreel said it is possible to delay the start of glucocorticoids until the PET scan is performed in patients without visual symptoms or jaw claudication.

PET scans are also expensive, and it can be difficult to get insurance coverage in the United States. However, other imaging modalities could potentially be used in similar ways, Warrington said.

"One could potentially extrapolate to say that if there is difficulty with accessing PET scan, we could use other modalities like CT or MRI basically to see whether the aorta is inflamed or not."

Moreel disclosed no relevant financial relationships. Warrington has received compensation for consulting activities with Sanofi. Eli Lilly, Kiniksa and Bristol-Myers Squibb have provided support to the Mayo Clinic for clinical trials related to GCA, of which Warrington served as sub-investigator.

Ann Intern Med. Published online October 2, 2023. Abstract

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