Glial fibrillary acidic protein IgG related myelitis: characterisation and comparison with aquaporin-4-IgG myelitis

IgG directed against the α-isoform of glial fibrillary acidic protein (GFAP-IgG) predicts a distinct corticosteroid-responsive meningoencephalomyelitis termed autoimmune GFAP astrocytopathy, when detected on cerebrospinal fluid (CSF).1 Optic disc oedema and tremor are common accompaniments. The MRI hallmark is a striking linear perivascular enhancement radially oriented around the ventricles (radial enhancement), while the myelitis component is generally associated with a longitudinally extensive T2 lesion on spinal cord MRI, similar to that typically encountered in aquaporin-4-IgG (AQP4-IgG) related myelitis.1–3 We compared the clinical, laboratory and MRI features of GFAP-IgG and AQP4-IgG related myelitis. ### Patient ascertainment We retrospectively identified GFAP-IgG seropositive patients seen at the Mayo Clinic ( 1 January 2000 to 31 December 2017). Inclusion criteria were as follows: (1) serum/CSF demonstrating GFAP pattern by indirect immunofluorescence with GFAPα specificity confirmed by cell-based assay, as previously described;1 (2) first myelitis episode; (3) serum sample negative for myelin oligodendrocyte glycoprotein-IgG (MOG-IgG) and AQP4-IgG using previously described methodology4 5; (4) adequate clinical data available. Nine patients with GFAP-IgG myelitis were included in a prior report.1 Two patients with dual positivity in serum for AQP4-IgG and GFAP-IgG were excluded. Medical records were reviewed and compared with 41 patients from a previously identified cohort of AQP4-IgG seropositive patients at the first episode of clinical myelitis who tested negative for GFAP-IgG (41 tested) and MOG-IgG (13 tested).5 Improvement was defined as subjective improvement reported by the patient with objective improvement confirmed by the physician. ### Neuroimaging All available MRI sequences obtained within 4 months of myelitis onset were reviewed by one neurology investigator (ES/EPF) and one neuroradiologist (TJK/KNK/PPM) as described previously.5 Consensus was achieved in situations of disagreement. ### Statistical analysis Wilcoxon rank-sum test or χ2/Fisher’s exact test was used as appropriate for comparison (JMP 8.0 software). Fifty-four patients with myelitis were included: GFAP-IgG positive, …