Histopathological characterization of the neuroglial tissue in ovarian teratoma associated with anti‐N‐methyl‐D‐aspartate (NMDA) receptor encephalitis

Anti‐N‐methyl‐D‐aspartate (NMDA) receptor encephalitis is a rare but occasionally fatal limbic encephalitis that may be accompanied by ovarian teratoma. Since the neuroglial tissue within the teratoma may be involved in the pathogenesis of this encephalitis, we attempted morphological and immunohistochemical characterization of the neuroglial tissue in four cases of ovarian teratoma associated with anti‐NMDA receptor encephalitis and 12 control cases, i.e., six consecutive cases of immature teratoma and six cases of mature teratoma with an abundant neuronal component, focusing mainly on NMDA receptor‐expressing neurons. NMDA receptor‐expressing neurons, being observed in all of the cases analyzed, were significantly densely aggregated ( P = 0.030, Wilcoxon test) and relatively smaller in size in the encephalitis‐associated cases than in the control cases, and the Ki‐67 labeling index of neuroglial cells with these neurons was significantly higher in the encephalitis‐associated cases ( P = 0.004, Wilcoxon test). In the cases with encephalitis, aggregation of B‐cells within or around the neuroglial tissue was also observed. Our present findings may be useful for more accurate diagnosis of anti‐NMDA receptor encephalitis and contribute to a better understanding of the pathogenesis.