Giant Cell Arteritis Diagnosis in Glucocorticoid-Treated Patients: Utility of PET/CT

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Although GCA is typically a clinical diagnosis, which is supported by a positive TAB finding, biopsy specimens may be falsely negative.
Although GCA is typically a clinical diagnosis, which is supported by a positive TAB finding, biopsy specimens may be falsely negative.

The utility of positron emission tomography (PET) and computerized tomography (CT) imaging to complement temporal artery biopsy (TAB) in patients with newly diagnosed giant cell arteritis (GCA) who are receiving glucocorticoid therapy remains equivocal, according to the results of a recent prospective Canadian study published in The Journal of Rheumatology.

Although GCA is typically a clinical diagnosis that is supported by a positive TAB (TAB+) finding, biopsy specimens may be falsely negative (TAB–). In cases of suspected GCA and TAB–, PET and CT scans are often used to confirm the diagnosis.

Patients with newly diagnosed GCA who had recently initiated glucocorticoid treatment underwent TAB and PET/CT scans. Uptake of 18F-fluorodeoxyglucose (FDG) was scored in 8 vascular territories and summed overall to yield a total score in all participants.

A total of 28 patients with GCA and 28 matched controls were included in the study. Of the 28 patients with GCA, 18 were TAB+. Whole-body PET/CT scans were taken in all 28 patients with GCA after a mean 11.9 days' treatment with high-dose prednisone and were compared with images from the 28 controls. The mean total PET/CT vascular uptake score was significantly higher in participants with GCA vs controls (10.3 ± 2.7 vs 7.7 ± 2.6; P =.001). Mean FDG uptake in 6 of the 8 vascular territories was significantly higher in patients with GCA vs controls. PET/CT scores in patients with GCA who were TAB+ and TAB– were similar.

The optimal cutoff for differentiating GCA cases from controls was a total PET/CT score ≥9, with an area under the receiver-operating characteristic curve of 0.75, a sensitivity of 71.4%, and a specificity of 64.3%. In patients with GCA, these values were associated with greater total PET/CT scores: systemic symptoms (P =.015), lower hemoglobin levels (P =.009), and higher platelet counts (P =.008).

The investigators concluded that, although vascular FDG uptake scores were increased in most patients with GCA despite glucocorticoid exposure, the sensitivity and specificity of PET/CT scans in this setting were lower than the values previously reported. Additional studies designed to evaluate the influence of specific steroid doses and duration of FDG uptake are warranted.

Reference

Clifford AH, Murphy EM, Burrell SC, et al. Positron emission tomography/computerized tomography in newly diagnosed patients with giant cell arteritis who are taking glucocorticoids [published online September 15, 2017]. J Rheumatol. doi: 10.3899/jrheum.170138

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