Immune checkpoint inhibitor induced anti-glutamic acid decarboxylase 65 (Anti-GAD 65) limbic encephalitis responsive to intravenous immunoglobulin and plasma exchange

Immune checkpoint inhibitors have made significant advances in available cancer treatment options towards progression-free and overall survival in cancer patients by potentiating own anti-tumor immune response. Anti-programmed death (PD-1) and anti-cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) have been increasingly associated with neurologic complications. LE is a rare complication and like many complications secondary to immunotherapy, there is no standard for evaluation and treatment. Anti-GAD65-associated LE has been associated with thymic carcinoma. We describe a patient who presented with progressive memory loss 2 weeks after her third cycle of Ipilimumab and Nivolumab with associated elevated Anti-GAD65 levels. Treatment with IVIG and PLEX led to complete resolution of her symptoms and improvement in her brain imaging and CSF findings.