Role of F-18 FDG-PET CT scan in the evaluation of medium vessel vasculitis

BACKGROUND: Medium vessel vasculitis (MVV), including polyarteritis nodosa (PAN), poses a diagnostic challenge due to its non-specific symptoms. While F-18 FDG PET/CT is well-established in large vessel vasculitis, its role in MVV remains unclear. We aimed to characterize the patterns of F-18 FDG uptake and evaluate the sensitivity of F-18 FDG PET/CT in patients with MVV. METHODS: We conducted a retrospective cohort study of patients with biopsy or imaging evidence of MVV who underwent F-18 FDG PET/CT at Mayo Clinic sites. F-18 PET/CT findings were correlated with clinical features, biopsy results, and other imaging. Logistic regression was used to assess predictors of F-18 FDG PET/CT positivity. RESULTS: Thirty-eight patients were included in the study; 23 (60.5%) were male and 32 (86.5%) were white, with a mean age at diagnosis of 58 years. Biopsies were done in 25 patients and showed evidence of vasculitis in 16 (64%). F-18 FDG PET/CT scans showed evidence of abnormal tracer uptake in 14 patients (36.8 %). Common F-18 PET/CT findings included uptake in lower extremity vessels (10), muscles (7), and upper extremity vessels (5). The most common pattern of muscle uptake was linear (6/7). Glucocorticoid use prior to F-18 FDG PET/CT was common and reported in 17. F-18 FDG PET/CT sensitivity was significantly higher in patients without prior glucocorticoid use (47.6% vs. 5.9%, p = 0.01). CONCLUSION: F-18 FDG PET/CT scans can show characteristic findings in MVV, with predominant involvement of lower extremity vessels and muscle uptake. However, it has limited sensitivity, and this can be further influenced by glucocorticoid use.