Paediatric myelin oligodendrocyte glycoprotein antibody-associated disease with NMDA receptor encephalitis: overlap syndrome and challenges in the antibody testing

We report the case of a middle childhood female child who presented with acute encephalopathy following multiple episodes of projectile vomiting and subsequently developed progressive cognitive decline, behavioural changes, visual impairment and motor regression. Neurological evaluation and imaging revealed multifocal demyelination with bilateral optic neuritis. Further work-up uncovered the coexistence of myelin oligodendrocyte glycoprotein antibody disease (MOGAD) and <i>N</i>-methyl-d-aspartate receptor encephalitis. Early initiation of immunotherapy with intravenous methylprednisolone and intravenous immunoglobulin led to significant clinical improvement. The case underscores the importance of screening for coexisting autoimmune conditions in demyelinating disorders, given the therapeutic and prognostic implications.