Pembrolizumab-Induced Myocarditis and Delayed Acute Inflammatory Demyelinating Polyradiculoneuropathy

Pembrolizumab is an immunotherapeutic agent used in various malignancies including metastatic melanoma. While immunotherapies are effective in treating several malignancies, they do come at the expense of inadvertent side effects. The numerous side effects of pembrolizumab, including, but not limited to, adrenal insufficiency, myocarditis, and pancreatitis, are well documented in clinical literature. In this case report, we describe a unique presentation of myocarditis and acute inflammatory demyelinating polyradiculoneuropathy secondary to pembrolizumab. While both side effects of pembrolizumab are well known, the delayed presentation of symptoms is of particular interest in our case report. We hope to inform the clinical community on the pharmacokinetics of pembrolizumab causing the delayed onset of symptoms.