[18F]FDG PET/CT value in the diagnostic evaluation of patients with polyarteritis nodosa.

PURPOSE: Polyarteritis nodosa (PAN) is a rare necrotizing vasculitis of medium-sized vessels with heterogeneous presentations and a challenging diagnosis. While [18F]FDG PET/CT is established in large-vessel vasculitis, its role in PAN remains unclear. A distinctive “ant-farm” uptake pattern has recently been associated with PAN. This study assessed the diagnostic value of [18F]FDG PET/CT in PAN. METHODS: Patients diagnosed with PAN who underwent [18F]FDG PET/CT between 2010 and 2025 were retrospectively included. Scans were blindly reviewed by two nuclear medicine physicians using a standardized grid. Abnormal uptakes, including the “ant-farm” pattern, were systematically recorded and correlated with clinical, biological, and histopathological data. RESULTS: Forty-seven patients were included. Abnormal uptake was frequently found in the bone marrow (83%), lymph nodes (40%), and spleen (34%). Abnormal vascular uptake was observed in 36% of cases, predominantly in the femoral and tibial arteries. The “ant-farm” pattern was identified in 34% of patients with excellent inter-observer reproducibility (κ = 0.80). It was more frequent with recent PET/CT devices and whole-body acquisitions and was associated with higher C-reactive protein levels and fewer PAN-suggestive biopsies. Distinct uptake patterns were observed in etiologies of secondary PAN, including VEXAS syndrome. CONCLUSION: [18F]FDG PET/CT is a valuable diagnostic tool in PAN and may also help identify secondary causes. The consistent “ant-farm” pattern may help distinguish patients with more inflammatory features, negative biopsy results and less PAN-related organ involvement.