LAUSR

OBJECTIVE 18F-fluorodeoxyglucose positron emission tomography with computed tomography (FDG-PET/CT) is widely used in patients with large-vessel vasculitis. The benefits of FDG-PET/CT in polyarteritis nodosa (PAN) has only ever been assessed in three case reports. Our aim was to describe FDG-PET/CT findings in 10 patients with newly diagnosed PAN. METHODS This was a retrospective study of patients with PAN who underwent FDG-PET/CT at diagnosis, between 2017 and 2020. The FDG-PET/CT data were analysed retrospectively. RESULTS Ten patients were included: nine men and one woman with a median age of 67 (43-78) years. PAN was diagnosed according to ACR criteria in nine patients, and histologically in one case. All patients had high C-reactive protein levels (median, 223 mg/l). The main FDG-PET/CT abnormality was increased tracer uptake in the muscles, particularly in the connective tissue (perimysium, epimysium) (n = 7), in linear (n = 5) or focal (n = 2) patterns. Increased FDG uptake in large-diameter vessels was observed in four patients, in the humeral (n = 4), femoral (n = 1) and the common interosseous arteries (n = 1). Nine patients had bone-marrow FDG uptake, six had splenic FDG uptake. Three had synovitis and three had lymph-node uptake. One patient had subcutaneous FDG uptake, with a "leopard skin" appearance. CONCLUSIONS FDG-PET/CT seems to be a useful non-invasive imaging technique for diagnosing PAN, particularly in patients with non-specific systemic features. Tracer uptake in muscular connective tissue seems to be a recurrent sign in patients with PAN and may be pathognomonic.