Pembrolizumab-Induced Myasthenia Gravis and Peripheral Neuropathy: A Case Series

Pembrolizumab is a monoclonal antibody that targets the programmed cell death protein 1 (PD-1) receptor on T-cells, thereby enhancing the antitumor immune response. Pembrolizumab has been shown to improve survival in various cancers, but it can also cause immune-related adverse events (irAEs), which can affect any organ system. We report two cases of rare but serious irAEs caused by pembrolizumab: myasthenia gravis (MG) and peripheral neuropathy. Both patients presented with neuromuscular symptoms after receiving pembrolizumab for their advanced cancers. They were diagnosed with MG and peripheral neuropathy based on their clinical features, laboratory tests, and unremarkable imaging. Treatment involved discontinuing pembrolizumab and initiating immunosuppressive and supportive therapies. Both patients experienced improvement in their symptoms and quality of life once pembrolizumab was permanently discontinued and supportive therapies were in place. These cases highlight the importance of recognizing and managing rare irAEs of pembrolizumab, such as MG and peripheral neuropathy. Early diagnosis and treatment can improve outcomes and reduce morbidity. Furthermore, these cases emphasize the need for continued post-marketing surveillance to accurately assess the risk of less frequent adverse drug reactions seen in patients on pembrolizumab. Knowledge of these adverse reactions is important when discussing the pros and cons of this novel therapy with patients.