Nivolumab-induced Lambert-Eaton myasthenic syndrome: an immune-related adverse event in nonsmall cell lung cancer.

Nivolumab is an anti-programmed cell death protein 1 (anti-PD-1) monoclonal antibody and was the first immune checkpoint inhibitor drug approved for use in advanced non-small cell lung cancer (NSCLC). In this report, we describe a rare case of Lambert-Eaton myasthenic syndrome (LEMS), which developed as a side effect of nivolumab in a patient with metastatic lung squamous cell carcinoma. Our patient, who was previously treated with nivolumab for metastatic squamous cell carcinoma of the lung, appeared with a headache, swollen face, dysarthria, asthenia, xerostomia, and drooping eyelid. Early testing indicated no thymomas or newly developing tumors in whole-body scans, and the blood workup was normal. We came to the conclusion that nivolumab-induced LEMS was the cause of the symptoms after performing nerve conduction investigations ruling out other differentials. We believe our clinical experience of this rare and unexpected adverse event should be shared.