[18F]FDG PET/CT imaging in Polyarteritis Nodosa-spectrum vasculitis.

Polyarteritis nodosa (PAN) is a medium-vessel vasculitis that may lead to severe complications and whose diagnosis remains challenging. While [18F]FDG PET/CT (FDG PET/CT) has become a key imaging modality in giant cell arteritis, it also appears promising for diagnosing PAN. This review summarizes current evidence on the use of FDG PET/CT in PAN-spectrum vasculitis, focusing on nuclear imaging features that may support diagnosis. FDG uptake involving medium-sized arteries, especially in the extremities, is a characteristic finding suggestive of PAN. Additionally, a distinct heterogeneous muscular pattern combining linear and focal uptake-known as the "ant-farm" (or "dirty muscle") pattern-appears to be associated with PAN-spectrum vasculitis and may indicate vasculitic myopathy, although its specificity and biological basis remain incompletely understood. FDG PET/CT may also reveal imaging findings suggestive of secondary PAN. Finally, its role in disease monitoring and in the evaluation of suspected relapse remains to be clarified. Based on these promising findings, FDG PET/CT may progressively emerge as a biomarker of PAN-spectrum vasculitis, particularly when other tests are inconclusive.