The Clinical Impact of Using 18F-FDG-PET/CT in the Diagnosis of Suspected Vasculitis: The Effect of Dose and Timing of Glucocorticoid Treatment

18F-Fluorodeoxyglucose positron-emission tomography (18F-FDG-PET) with computed tomography (CT) is effective for diagnosing large vessel vasculitis, but its usefulness in accurately diagnosing suspected, unselected vasculitis remains unknown. We evaluated the feasibility of 18F-FDG-PET/CT in real-life cohort of patients with suspicion of vasculitis. The effect of the dose and the timing of glucocorticoid (GC) medication on imaging findings were in special interest. 82 patients with suspected vasculitis were evaluated by whole-body 18F-FDG-PET/CT. GC treatment as prednisolone equivalent doses at the scanning moment and before imaging was evaluated. 38/82 patients were diagnosed with vasculitis. Twenty-one out of 38 patients had increased 18FFDG accumulation in blood vessel walls indicating vasculitis in various sized vessels. Vasculitis patients with a positive vasculitis finding in 18F-FDG-PET/CT had a significantly shorter duration of GC use (median = 4.0 vs 7.0 days, P = 0.034), and they used lower GC dose during the PET scan (median dose - 15.0 mg/day vs 40.0 mg/day, p = 0.004) compared to 18F-FDG-PET/CTnegative patients. Vasculitis patients with a positive 18F-FDG-PET/CT result had significantly higher C-reactive protein (CRP) than patients with a negative 18F-FDG-PET/CT finding (mean value = 154.5 vs 90.4 mg/L, p = 0.018). We found that 18F-FDGPET/CT positivity was significantly associated with a lower dose and shorter duration of GC medication and higher CRP level in vasculitis patients. 18F-FDG-PET/CT revealed clinically significant information in over half of the patients and was effective in confirming the final diagnosis.