Anti-NMDA receptor encephalitis in an adolescent with a cryptic ovarian teratoma

Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis is an autoimmune disease frequently associated with ovarian teratomas. In cases where an ovarian teratoma is identified, treatment involves prompt removal of the ovarian teratoma, resulting in significant clinical improvement and decreased incidence of relapse. We present the case of a 14-year-old female patient admitted for progressively worsening psychiatric and neurological status, diagnosed with anti-NMDAR encephalitis, and negative initial imaging for ovarian pathology. She was in the hospital for 8 months requiring admission to the intensive care unit and multiple courses of immunotherapy before clinical improvement. Three months after discharge, she was readmitted with clinical relapse and repeat imaging showed an ovarian teratoma. Removal of the teratoma resulted in sustained clinical improvement with return to baseline and no further relapse. Our case report highlights the importance of maintaining a high suspicion for an underlying ovarian teratoma in a female patient with anti-NMDAR encephalitis, even when initial imaging is negative. Currently, there are limited data on recommendations for repeat imaging. Therefore, we recommend repeat imaging in patients resistant to multiple lines of treatment or presenting with clinical relapse.