Prolonged Treatment in a Case of Anti-N-Methyl-D-Aspartate Receptor Encephalitis.

Background: Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is a rare autoimmune encephalitis. The proposed mechanism relates to the circulating tumor-induced antibody, so the treatment includes tumor removal and immunotherapy. This report is aimed at describing a case of anti-NMDAR encephalitis in a female patient with an ovarian teratoma who required prolonged immunotherapy. Case Report: A 17-year-old female presented with a fever before hospital admission, then progressed to neurologic and psychiatric symptoms. The indirect immunofluorescence antibody (IFA) test revealed positive anti-NMDAR immunoglobulin G (IgG) in serum and cerebrospinal fluid (CSF) samples. The patient was diagnosed with teratomas on both ovaries at different times. Two surgeries were performed to remove the tumors. The patient received systemic corticosteroids and 30 sessions of plasmapheresis. After approximately 2 months of treatment, the patient improved significantly and was discharged. At follow-up, she showed good clinical recovery, although mild residual cognitive impairment was noted on formal assessment. Conclusions: This case highlights that, in young women with anti-NMDAR encephalitis, early and thorough evaluation for ovarian teratoma is essential. If recovery remains incomplete after initial surgery and immunotherapy, repeat assessment for occult, residual, or contralateral lesions should be considered. Careful preoperative lesion assessment and fertility-preserving surgical planning may help reduce missed lesions while minimizing unnecessary ovarian tissue loss.