Fulminant Immune Checkpoint Inhibitor‐Related Encephalitis (ICI‐Encephalitis) Presenting Rapidly After First Infusion of Nivolumab: A Case Report

Introduction: Immune checkpoint inhibitors (ICIs) are increasingly used in oncologic clinical practice, leading to a corresponding rise in immune-related adverse events (irAEs). In this context, we present a case of fulminant ICI-associated encephalitis (ICI-encephalitis) presenting within 24 h after a single administration of nivolumab (a PD-1 inhibitor), in a patient with recurrent Hodgkin lymphoma. Case Presentation: After receiving outpatient nivolumab combined with brentuximab (an antibody-drug conjugate), the patient presented with altered mental status, status epilepticus, and abnormal signal in the bilateral temporal lobes as shown on brain magnetic resonance imaging (MRI). Lumbar puncture found pleocytosis and slight elevation in protein; there was no evidence of abnormal autoantibodies or pathogenic infection. Following multidisciplinary consultation, the patient was ultimately diagnosed with ICI-encephalitis and began on empiric treatment with intravenous methylprednisolone dosed 1 g/day for 5 days, followed by 5 days of intravenous immunoglobulin (IVIG). The patient experienced resolution of electrographic seizures and gradual improvement of mental status toward baseline but had persistent short-term memory loss and did not experience complete brain MRI recovery. Ultimately, hospice placement was pursued after goals of care discussions with the patient's spouse, and the patient expired within 1 month of discharge. Conclusion: This case serves as a safety signal for rapidly presenting ICI-encephalitis following nivolumab.