We describe a case of Acute Inflammatory Demyelinating Polyneuropathy (AIDP) in a patient who was being treated with immune checkpoint inhibitor therapy. Neurologists are unfamiliar with this serious complication of these agents, and that steroids are an option for therapy.

A 67-year old male with history of metastatic urothelial carcinoma, on palliative treatment with pembrolizumab infusions (4 cycles over the preceding 10 weeks), presented with 1 week of worsening weakness for which he required intubation. EMG/Nerve conduction studies revealed findings consistent with AIDP. Cerebrospinal fluid revealed albuminocytologic dissociation. He was started on intravenous immune globulin (IVIG) for a five-day course, and was also started on pulse dose intravenous methylprednisolone, 1 gram per day for four days, since this was considered a side effect of checkpoint inhibitor therapy. Pembrolizumab infusions were permanently halted. The patient's family decided to withdraw care based on his poor oncologic prognosis after a week of admission, during which time no clear neurological improvement had been seen. 

Pembrolizumab is an anti-PD1 (Programmed Cell Death-1) antibody that is seeing increasing adoption for treatment of metastatic solid organ cancers. There have been a few reports of neuropathies in the setting of Pembrolizumab use, and the standard approach is to stop further infusions of these agents. For AIDP, administration of intravenous steroids in addition to IVIG or plasma exchange therapy appears reasonable, given we use steroids in managing other immune-mediated complications of these agents such as colitis. However, high quality evidence is lacking.

Neurologists must be aware of the risk of AIDP with the use of pembrolizumab and other immune checkpoint inhibitors, and must consider the use of intravenous steroids in addition to IVIG or plasma exchange.