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Glial fibrillary acidic protein (GFAP) astrocytopathy is a rare autoimmune inflammatory disorder of the central nervous system which can cause meningitis, encephalitis, and myelitis. It is typically steroid responsive, although may have a relapsing course requiring long-term treatment. Median age of onset is in the 4^th decade of life. Patients commonly present with headache and encephalopathy, although tremor and ataxia have rarely been reported.

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One year prior to presenting to our clinic, an 84 year-old man abruptly developed confusion, fatigue, apathy, and anorexia. Symptoms were attributed to new-onset depression and he was admitted to a psychiatric facility for electroconvulsive therapy and trials of psychotropic medications. Following discharge, he developed visual hallucinations, delusions, and a more pronounced decline in cognition, meeting criteria for dementia. At that time, he was given a diagnosis of Dementia with Lewy Bodies (DLB), started on donepezil, and referred to our movement disorders clinic. At our initial visit, his exam was notable for symmetric parkinsonism with resting tremor, severe disturbance of gait, loss of postural reflexes, and a Montreal Cognitive Assessment score of 11/30. Given his relatively rapid course, a lumbar puncture was obtained which revealed elevated protein, a lymphocytic pleocytosis, six oligoclonal bands, and positive GFAP antibody (CBA and IFA titer). He was treated with a course of high dose IV steroids followed by oral steroids and rituximab. Cognition has improved significantly with these treatments, though with only modest improvement in mobility.

To our knowledge, this gentleman represents the oldest reported age of onset of GFAP astrocytopathy. Despite one year of untreated symptoms, our patient improved with immunosuppression. GFAP astrocytopathy should be considered as a rare cause of rapid-onset dementia and in the differential diagnosis of DLB, particularly given the potential for reversal of some symptoms.