Introduction Autoimmune glial fibrillary acidic protein (GFAP) astrocytopathy is scarce and usually presents as meningoencephalomyelitis. Here, we offer the case of an atypical presentation of GFAP-astrocytopathy. Case Presentation We report the case of a 26-year-old woman admitted to our neurology department for a 3-week progressive and worsening neurologic picture, with secondary worsening. Initial imaging showed a Mild Encephalitis with Reversible Splenium of corpus callosum lesion (MERS). Full infectious and autoimmune workup then revealed positivity of GFAP antibodies, leading us to diagnose GFAP astrocytopathy. Discussion Our case is the first reported association between MERS and GFAP astrocytopathy in an adult patient. Clinical presentation of GFAP astrocytopathy usually includes various neurologic symptoms and can lead to misdiagnosis.