Objectives:To report the clinical, biological, imaging features, and the clinical course of a French cohort of patients with glial fibrillar acidic protein (GFAP) autoantibodies.Methods:We retrospectively included all patients tested positive for GFAP antibodies in the cerebrospinal fluid, by immunohistochemistry and confirmed by cell-based assay using cells expressing human GFAPα, since 2017, from two French referral centers.Results:We identified 46 patients with GFAP antibodies. Median age at onset was 43 years, and 65% were men. Infectious prodromal symptoms were found in 82%. Other auto-immune diseases were found in 22% of patients, and coexisting neural autoantibodies in 11%. Tumors were present in 24%, and T cell dysfunction in 23%. The most frequent presentation was subacute meningoencephalitis (85%) with cerebellar dysfunction in 57% of cases. Other clinical presentation included myelitis (30%), visual (35%) and peripheral nervous system involvement (24%). MRI showed perivascular radial enhancement in 32%, periventricular T2 hyperintensity in 41%, brainstem involvement in 31%, leptomeningeal enhancement in 26%, and reversible splenial lesions in 4 cases. 33/40 patients had a monophasic course, associated to a good outcome at last follow-up (Rankin Score≤2: 89%), despite a severe clinical presentation. Adult and pediatric features are similar. Thirty-two patients were treated with immunotherapy. 11/22 patients showed negative conversion of GFAP antibodies.Interpretation:GFAP auto-immunity is mainly associated with acute/subacute meningoencephalomyelitis with prodromal symptoms, for which tumors and T cell dysfunction are frequent triggers. The majority of patients followed a monophasic course with a good outcome.

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High-level improvement of diagnostic certainty and management is provided by selective and hierarchical implementation of florbetaben PET into current standard practices for the most complex dementia cases.