Pembrolizumab-induced vasculitis demonstrated by FDG-PET/CT.

A 76-year-old man with a history of malignant pleural mesothelioma treated with pembrolizumab underwent FDG-PET/CT for restaging. The images demonstrated FDG uptake overlying the right hepatic and splenic artery, which were new from the previous FDG-PET/CT 2.5 years prior before the patient started pembrolizumab, suspicious for vasculitis. A follow-up MRI supported the diagnosis with evidence of celiac, splenic, common hepatic, and right hepatic artery involvement. Pembrolizumab was discontinued and the patient received a short course of oral glucocorticoids. Subsequent FDG-PET/CT performed 14 months after initiation of treatment for vasculitis demonstrated resolution of vasculitis. Immune checkpoint inhibitors can cause vasculitis, which can be recognized on FDG-PET/CT and lead to appropriate treatment.