Immature ovarian teratoma with anti-NMDA-receptor encephalitis in a 13-year-old Japanese female patient.

We report a 13-year-old Japanese female with ovarian teratoma due to anti-NMDAR encephalitis. The patient was admitted with psychiatric symptoms, including memory impairment, insomnia, binge eating and mouth and hand twisting, associated with constipation. Serum alphafetoprotein and neopterin levels were elevated 102 ng/mL and 19 pmol/mL, respectively. Electroencephalography showed epileptic spikes in frontal and temporal regions. Cerebrospinal fluid (CSF) examination exhibited a pleocytosis. Thereafter, her consciousness level immediately worsened. Brain magnetic resonance imaging (MRI) noted hyper intense lesions in bilateral hippocampi, she was diagnosed with limbic encephalitis. Abdominal echogram showed a solid right ovarian tumour. and also confirmed as a tumour by abdominal MRI. The next day, right ovariectomy was performed and she treated two courses of methyl-prednisolone steroid pulse with high-dose immunoglobulins. Later days, CSF analysis revealed anti- NMDAR antibodies. Pathological diagnosis of the tumour was immature round shaped grade 3 ovarian teratoma, measuring 11cm. Two years follow up after admission, she completely recovered and no neurological sequelae.