Unusual Presentation of a Rare Case of Immunotherapy Combination-Induced Encephalitis: A Case Report.

Introduction: Immune checkpoint inhibitors have revolutionized cancer treatment owing to their ability to activate cellular immune checkpoint pathways and mediate an antitumor activity. Due to their immunological actions, immune-related adverse events (irAEs) have become a concern. Neurological adverse events are rarely seen whether in the central or peripheral nervous system and can be potentially life-threatening. We present a rare case of occipital encephalitis following dual immunotherapy treatment in a patient with melanoma. Case Presentation: A 41-year-old man diagnosed with nodular melanoma of the right torso with axillary lymphadenopathies was treated with dual immunotherapy: nivolumab and ipilimumab. After 24 weeks, patient developed right homolateral hemianopia, and imaging findings correlated with occipital encephalitis. Autoantibodies were not detected. The patient was treated with steroids and exhibited radiological improvement of his encephalitis but maintained his right hemianopia. Conclusion: Neurological side effects of immunotherapy are not very common and range from mild to severe life-threatening symptoms. Previous analyses have shown that combination immunotherapy has a higher risk of side effects than monotherapy. Diagnosis of neurological manifestations is usually made by imaging, mainly brain magnetic resonance imaging or detection of autoantibodies in the CSF. The gold standard treatment is usually corticosteroids or rarely other molecules such as IVIg or monoclonal antibodies. The prognosis is usually favorable.