Brain Stem Encephalitis in a Patient With Recurrent Small Cell Lung Cancer Treated With Immune Checkpoint Inhibitor: Case Presentation and Review of the Literature.

Immunotherapy with checkpoint inhibitors (CPIs) has revolutionized the management of advanced cancer including advanced small cell lung cancer (SCLC). Unfortunately, those agents are not without adverse effects. Immune imbalance through enhanced cellular immune response may result in impaired endogenous immunological tolerance mechanisms that can result in a wide spectrum of immunological side effects also known as immune-related adverse events (irAEs). Scarce data are currently available about neurological immune-related adverse events (neuro irAEs), mainly obtained from clinical trials, case reports, or small case series. Most reported cases presented with nonspecific symptoms. It is important to recognize and promptly treat neuro irAEs, as it may be serious and even potentially fatal. We present a rare case of nivolumab induced brain stem encephalitis in a patient with advanced SCLC presented 10 months after starting treatment with symptoms of nystagmus, gait disturbance, and blurry vision. Nivolumab was held and the patient was started on oral steroids with tapering dose. The patient's symptoms gradually improved over a few weeks. Re-challenging with nivolumab six weeks later resulted in recurrence of symptoms and again the patient was prescribed oral steroids with tapering dose. She maintained response off treatment for six months. This case report is aimed to highlight the importance of clinically suspecting and promptly treating neurological irAE, when managing a patient with CPIs.