Immune-mediated encephalitis related to immune checkpoint inhibitor therapy is a rare but increasingly described condition that can cause significant morbidity. There are several reported cases in the literature but no previously described cases of immune-mediated cerebellitis. We describe a case of acute cerebellitis that developed in a 20-year-old man with primary refractory Hodgkin lymphoma being treated with the immune checkpoint inhibitor nivolumab. After exposure to 3 cycles of nivolumab, the patient had acute onset of headache, ataxia, nausea, and vomiting, with imaging findings of cerebellar edema, early tonsillar herniation, and early hydrocephalus. Immune-mediated cerebellar encephalitis was suspected and high-dose dexamethasone therapy (8 mg every 6 hours) was initiated. Within 4 days of dexamethasone therapy, his symptoms greatly improved with near-complete resolution of symptoms after a 4-week taper. Differential diagnosis of his condition included viral cerebellitis and paraneoplastic cerebellar degeneration. In cerebellar encephalitis suspected to be due to immune checkpoint inhibitor therapy, prompt recognition and early initiation of high-dose corticosteroids is essential for symptom resolution and treatment success, including the prevention of hydrocephalus and tonsillar herniation. Currently, there are no evidence-based guidelines to guide the initial dose, type, or duration of corticosteroids. Further investigation is needed in the pathogenesis and treatment of cerebellar encephalitis related to immune checkpoint inhibitor therapy to effectively treat this rare, disabling condition.
Keywords: CSF, cerebrospinal fluid; GAD, glutamic acid decarboxylase; ICI, immune checkpoint inhibitor; MRI, magnetic resonance imaging; PCD, paraneoplastic cerebellar degeneration; PD-1, programmed death-1; irAE, immune-related adverse effect.