Fluorodeoxyglucose positron emission tomography-computed tomography findings in a first series of 10 patients with polyarteritis nodosa.

Objective: 18F-fluorodeoxyglucose PET/CT (FDG-PET/CT) is widely used in patients with large vessel vasculitis. The benefits of FDG-PET/CT in 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 years (range 43-78). PAN was diagnosed according to ACR criteria in nine patients and histologically in one. All patients had high CRP 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), and 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 common interosseous arteries (n = 1). Nine patients had bone marrow FDG uptake and 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.