October 07, 2015
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FDG PET/CT may aid diagnosis of GCA in patients prior to glucocorticoid exposure

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The diagnosis of giant cell arteritis may be aided by the use of fluorodeoxyglucose positron emission tomography/CT in patients who have not been exposed to glucocorticoids, according to recently published research.

Researchers acquired fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT images from 18 patients with giant cell arteritis (GCA) who were scanned between November 2009 and December 2012 in a retrospective study. Patients with GCA were matched for age and sex with 18 patients with elevated C-reactive protein (CRP) to compare with another inflammatory group, with 19 patients with a vascular calcification score on low-dose CT (LDCT) greater than 2 and matched for sex only with 16 patients with no inflammation or vascular calcification on LDCT.

All FDG PET/CT scans were performed on a Siemans Biograph mCT camera system following a standard protocol. Two of the study authors, blinded to patient data, interpreted the images with high interoperator agreement. Three methods and subsets were used: method 1a was visual only, 1b was graded 0 to 4 and compared vascular vs. liver uptake, method 2a used a quantitative standardized uptake value (SUVmax) of the aorta, method 2b used a quantitative SUVmax ratio of the aorta to the liver, method 2c used a quantitative SUVmax ratio of the aorta to the superior caval vein and method 2d used a quantitative SUVmax ratio of the aorta to the inferior caval vein.

Significantly higher uptake in the vascular region of patients with GCA was observed compared to patients in the control groups. Uptake between patients in the three control groups did not vary significantly.

The sensitivity of method 1a, based on expert opinion, had 56% sensitivity and 98% specificity. When patients who received glucocorticoids were excluded, sensitivity increased to 75%. Method 1b yielded the highest diagnostic accuracy when the definition of a positive scan included the presence of an arterial structure with higher visual uptake than the liver. The sensitivity was 83%, specificity was 91% and exclusion of patients who received glucocorticoids resulted in a sensitivity increase to 92%. When a positive judgement was made in the presence of a vascular FDG uptake similar to the liver, the sensitivity was 100% while specificity was decreased to 51%.

“Based on our results, a visual grading method with an arterial FDG uptake higher than the liver FDG uptake has the highest diagnostic accuracy for GCA,” the researchers wrote. “It is also important to score the pattern of FDG uptake (focal vs. diffuse) and to correct for the presence of atherosclerosis.” – by Shirley Pulawski

Disclosure: The researchers report no relevant financial disclosures.