Case ReportsSevere Demyelinating Polyneuropathy and Cranial Neuropathy During Avelumab Treatment of Metastatic Merkel Cell CarcinomaBilić, Hrvoje MD∗; Sitaš, Barbara MD∗; Hančević, Mirea MD∗; Habek, Mario MD, PhD∗,†; Simetić, Luka MD‡; Bilić, Ervina MD, PhD∗,†Author Information ∗Department of Neurology, Clinical Hospital Centre Zagreb †School of Medicine, University of Zagreb ‡Department of Oncology, Clinical Hospital Centre Zagreb, Zagreb, Croatia. Address correspondence and reprint requests to Hrvoje Bilić, MD, Department of Neurology, Clinical Hospital Centre Zagreb, Kišpatićeva 12, 10000 Zagreb, Croatia; E-mail: [email protected] Conflicts of Interest and Source of Funding: The authors have no conflicts of interest to declare. We confirm that we have read the journal's position on issues involved in ethical publication and affirm that this report is consistent with those guidelines. All procedures performed in this study involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. Informed consent was obtained from the research subject included in this article. Clinical Neuropharmacology: 9/10 2021 - Volume 44 - Issue 5 - p 193-195 doi: 10.1097/WNF.0000000000000464 Buy Metrics Abstract Introduction Avelumab is a programmed death ligand 1–blocking monoclonal antibody used for the treatment of Merkel cell carcinoma (MCC), urothelial carcinoma, and other solid tumors. It acts as an immune checkpoint inhibitor and prolongs survival of MCC patients. Immune-mediated neurological adverse effects are rare and usually respond well to specific therapy. Methods and Results A case of a 70-year-old man with metastatic MCC is described in this study. The patient developed diplopia after the fourth dose of avelumab, which was then discontinued. Seven months later, therapy was reinitiated and followed by a new adverse neurological event: severe demyelinating polyneuropathy combined with ophthalmoplegia refractory to a plethora of immune suppressive/modulatory treatment regimes. Discussion This report of severe demyelinating polyneuropathy and cranial neuropathy associated with an anti–programmed death ligand 1 drug refractory to immune suppressive/modulatory treatments sheds a new light to evolving spectrum of immune checkpoint inhibitor immune-related neurological adverse events. Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.