Diagnostic and Therapeutic Challenges in Anti-NMDA Receptor Encephalitis Associated with an Ovarian Immature Teratoma

Background: Anti–N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is an autoimmune disorder characterized by antibodies against the NR1 subunit of the NMDA receptor. It predominantly affects young women and is frequently associated with ovarian teratomas. Early recognition, tumor removal, and immunotherapy are critical for favorable outcomes. Case Presentation: We report a 33-year-old woman with subacute headache, low-grade fever, generalized weakness, and mood disturbances, who developed generalized tonic–clonic seizures and cognitive impairment. Brain MRI and CSF were initially normal, and EEG showed diffuse slowing without epileptiform discharges. Pelvic imaging revealed a large right ovarian mass. She was treated with corticosteroids, plasmapheresis, and ultimately rituximab, alongside right salpingo-oophorectomy. Histopathology confirmed an immature teratoma. Anti-NMDAR antibodies were later detected in CSF, confirming the diagnosis. Following tumor removal and immunotherapy, she achieved complete neurological recovery and remained seizure-free at six months. Conclusion: This case highlights the diagnostic challenges of anti-NMDAR encephalitis, particularly when MRI and CSF are normal. Early tumor detection and removal, combined with prompt escalation to second-line immunotherapy when needed, are essential for favorable outcomes. Immature ovarian teratomas, although rare, can trigger severe disease and warrant careful evaluation in adult women presenting with acute neuropsychiatric symptoms.