Eosinophilic Fasciitis and Acute Encephalopathy Toxicity from Pembrolizumab Treatment of a Patient with Metastatic Melanoma.

Anti-PD-1 inhibitors have significant activity in metastatic melanoma. Responses often occur early and may be sustained. The optimal duration of treatment with these agents is unknown. Here, we report the case of a 51-year-old woman treated with pembrolizumab, as part of the Keynote-001 trial, as first-line treatment for metastatic disease. She experienced a complete response after 13.8 months of treatment with no adverse events. One month after the last drug infusion and 18 months from starting treatment, the patient presented with eosinophilic fasciitis. She then developed acute confusion and weakness, thought to be due to intracranial vasculitis. High-dose steroids were initiated with resolution of the fasciitis. Aspirin was commenced for presumed vasculitis with resolution of the neurologic symptoms. To our knowledge, there are no previous reports of eosinophilic fasciitis or cerebral vasculitis due to anti-PD-1 agents. This case demonstrates that toxicity may occur in association with pembrolizumab treatment after a prolonged period of treatment without toxicity. Future trials should explore the optimal duration of treatment with pembrolizumab.