Refractory anti–NMDA receptor encephalitis driven by a contralateral ovarian teratoma following unilateral oophorectomy: a case report

Introduction and Importance: Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is a rare autoimmune encephalitis frequently associated with ovarian teratomas. Persistent or residual teratomas may function as ongoing antigenic reservoirs, resulting in refractory disease despite aggressive immunotherapy. Recognition of residual ovarian pathology is therefore critical for effective disease control. Case Presentation: A 27-year-old nulligravida with a prior right salpingo-oophorectomy for mature teratoma presented with progressive psychiatric symptoms, seizures, and respiratory failure requiring intensive care. Cerebrospinal fluid analysis confirmed anti-NMDAR encephalitis. Despite immunotherapy, neurological improvement was limited. Repeat imaging identified a residual contralateral ovarian cyst, and subsequent laparotomy with cystectomy confirmed a mature teratoma. The patient received high-dose corticosteroids, intravenous immunoglobulin, and rituximab, with gradual but prolonged neurological recovery following tumor resection. Clinical Discussion: Ovarian teratomas containing neuroglial tissue serve as a source of NMDA receptor antigens, perpetuating autoimmune activation. Diagnosis is frequently delayed by initial psychiatric presentations and radiologically occult tumors. This case highlights the limitation of single-time-point imaging and underscores the importance of repeat multimodal pelvic evaluation in patients with refractory disease. Conclusion: This case demonstrates that postoperative residual or contralateral ovarian teratomas can drive persistent anti-NMDAR encephalitis despite immunotherapy. Repeat imaging should be strongly considered in refractory cases, and complete tumor resection remains essential to interrupt the autoimmune process. Early multidisciplinary collaboration between gynecology, neurology, and intensive care teams is crucial to optimize neurological outcomes.