GAD65 Autoimmune Encephalitis: A Cause of Rapidly Evolving Frontotemporal Atrophy.

We describe a patient who presented with subacute onset of short-memory impairment, disorientation, and gait instability, with progressive deterioration. Workup demonstrated glutamic acid decarboxylase antibody-related encephalitis. Aggressive immunotherapy with high-dose intravenous corticoids, followed by slow oral taper, plasmapheresis, rituximab, and cyclophosphamide did not halt disease progression. During follow-up, she developed a frontotemporal dementia phenotype. Serial imaging showed the appearance of marked atrophy of the frontal and anterior temporal regions. We conclude that glutamic acid decarboxylase antibody-related encephalitis may rarely present with a treatment-refractory frontotemporal phenotype.