Ovarian Teratoma After Treatment for Coexisting Anti-NMDA Receptor and Myelin Oligodendrocyte Glycoprotein Antibody-Associated Encephalitis.

Anti-N-methyl-d-aspartate receptor encephalitis (NMDARE) is an autoimmune encephalitis often associated with ovarian teratomas in adults but rarely in children. Myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) typically occurs in pediatric populations and may occasionally coexist with NMDARE. We report the case of a 6-year-old girl diagnosed with concurrent NMDARE and MOGAD. She presented with psychiatric symptoms and oral dyskinesia, and her magnetic resonance imaging findings were compatible with both NMDARE and MOGAD. Anti-NMDAR antibodies were detected in the cerebrospinal fluid, and anti-MOG antibodies were detected in the serum. Despite treatment with intravenous methylprednisolone and intravenous immunoglobulin, her symptoms persisted until plasma exchange and rituximab therapy, after which improvement was observed. Although no neoplastic lesion was identified during the acute phase, follow-up screening revealed a right ovarian teratoma 6 months after onset. Histopathology demonstrated neural tissue positive for both NR1 and MOG, along with infiltration of CD4-, CD8-, and CD68-positive cells. Few CD20-positive cells were observed, possibly reflecting prior rituximab therapy. To date, patients positive for both anti-NMDAR and anti-MOG antibodies have not been reported to have an associated ovarian teratoma. This is the first case of overlapping NMDARE and MOGAD with a posttreatment ovarian teratoma. Our findings highlight the importance of continued tumor surveillance in such cases, even in pediatric patients with coexisting antibodies.