To identify the chronic meningitis presentation of MOG IgG.

Meningitis is a rare manifestation of Myelin oligodendrocyte Glycoprotein (MOG) IgG Associated Disease.

Retrospective hospital-based case series from a university hospital in South India (2018 to 2023). Cases were included if presented with chronic meningitis and MOG IgG was positive (serum/CSF) and responded to immunotherapy.

We identified 3 (all females, age 17- 60year) cases. First case presented with symptoms and CSF findings suggestive of tuberculous meningitis (TBM) and antituberculous therapy (ATT) was started empirically, but symptoms recurred whenever steroids were tapered, hence ATT was continued for 2 years, later she presented with recurrence of symptoms and underwent multiple CSF studies and MOG IgG was detected on serum testing, (was negative in the first 2 testing). She had clinical, radiological and CSF improvement with IV methyl prednisolone, (IVMP) Inj cyclophosphamide and later on azathioprine. Second case was a 22-year-old girl presented with meningoencephalitis and arachnoiditis and was empirically started on ATT based on CSF finding, but continued to worsen despite adequate therapy, but responded to plasma exchange (considering alternate diagnosis of autoimmune meningitis). Subsequently she was initiated on IVMP followed by Inj Rituximab, later her serum was tested positive for MOG IgG, (earlier testing was negative). A 19-year girl presented with headache and vomiting and CSF was suggestive of TBM, started on empiric ATT, did not respond well, but developed optic neuritis which was thought to be ethambutol induced, but MOG IgG was positive (though sample at presentation was negative), responded well to IVMP followed by azathioprine.  M. tuberculosis was negative in all 3 cases.