Pearls & Oy-sters: Autoimmune Glial Fibrillary Acidic Protein Astrocytopathy Presenting as Encephalomyelitis With Leptomeningeal Enhancement

Autoimmune glial fibrillary acidic protein (GFAP) astrocytopathy is an uncommon diagnosis in the differential for leptomeningeal enhancement. This case highlights the presentation, imaging features, and investigations important for diagnosis of GFAP astrocytopathy to ensure timely treatment of this corticosteroid-responsive disease. A 50-year-old man from Hong Kong presented with 10 days of progressive urinary retention, dysarthria, diplopia, and gait ataxia after a viral illness. Initial nonenhanced MRI brain was negative. After he developed encephalopathy, repeat MRI with gadolinium on admission day 6 revealed diffuse basal and spinal cord leptomeningeal enhancement. This imaging pattern, in combination with CSF eosinophilia and epidemiologic risk factors, precipitated empiric treatment for tuberculosis meningitis (including dexamethasone). Extensive investigations for an alternate infectious, autoimmune, or malignant diagnosis were negative. Dexamethasone cessation after a gastrointestinal bleed led to clinical and radiologic deterioration. This prompted further CSF and serum testing, which showed positive CSF GFAP-IgG immunofluorescence assay (IFA) (1:128) solidifying the diagnosis of autoimmune GFAP astrocytopathy. Induction with high-dose corticosteroids, intravenous immunoglobulins, and rituximab produced clinical and radiologic remission. Autoimmune GFAP astrocytopathy is an autoimmune disorder with a characteristic perivascular radial enhancement imaging pattern. However, a variety of other clinical and radiologic presentations may be seen, including leptomeningeal enhancement and T2/FLAIR hyperintensities. Diagnosis is confirmed with CSF GFAP-IgG testing. We provide a differential diagnosis for leptomeningeal enhancement and highlight clinical pearls for the diagnosis and management of autoimmune GFAP astrocytopathy.