Autoimmune glial fibrillary acidic protein (GFAP) encephalitis is a novel disorder characterized for subacute neuropsychiatric symptom development and rapid remission with corticosteroid therapy. Here we describe a case of GFAP encephalitis presenting with renal cell carcinoma (RCC).

A 71-year-old man with a history of diabetic retinopathy and monoclonal gammopathy of undetermined significance (MGUS) presented for four months history of memory problems, intermittent word-finding difficulties and later development of auditory hallucinations requiring assistance with activities of daily living.

On admission, he was oriented to person, his language was affected with decreased fluency and difficulty following commands. On work up, metabolic causes, toxins, and nutritional deficiencies were ruled out. Brain MRI was degraded by motion artifacts, but no obvious abnormality was appreciated. Lumbar puncture was remarkable for leukocytosis (37 WBC), but infectious workup was negative. Creutzfeldt Jakob Disease was ruled out with a negative RT-QUiC following a 14-3-3 protein level elevation. Mayo autoimmune panel detected GFAP IgG (1:16, reference <1:2), with follow up imaging showing RCC confirmed on nephrectomy.

Patient was treated with daily intravenous methylprednisolone 1000mg for 5 days and showed improvement. However, the day after treatment was stopped, he had a rapid decline in cognition. Long term steroid treatment with 1mg/kg/day prednisone and steroid sparing agent, mycophenolate 500mg BID were started. Patient returned to baseline after four days and was discharged.

Although there is no specific diagnostic criteria, the identification of GFAP-IgG in serum or CSF is a marker of disease and the patient’s response to corticosteroid treatment further supports an autoimmune etiology. Further work is needed to create stringent diagnostic criteria and treatment protocols for GFAP encephalopathy and its associations with neoplasms.