N-Methyl-D-Aspartate (NMDA) Receptor Encephalitis Without Electroencephalogram Abnormalities or Cerebrospinal Fluid Pleocytosis Associated With a Tiny Ovarian Teratoma: A Case Report

N-methyl-D-aspartate (NMDA) receptor encephalitis is one of the autoimmune disorders characterized by neuropsychiatric symptoms, most commonly associated with ovarian teratoma. While detection of NMDA receptor antibody in cerebrospinal fluid (CSF) is the diagnostic standard, it is often limited by a delayed turnaround time. Abnormal electroencephalogram (EEG) findings and pleocytosis in CSF analysis are frequently observed, and computed tomography (CT) can aid in identifying an underlying ovarian teratoma. Here we report the case of a 36-year-old female who presented with acute psychosis, had a normal EEG and no CSF pleocytosis, and was later diagnosed with NMDA receptor encephalitis associated with a 7 mm ovarian teratoma. This case underscores the diagnostic challenges in the setting of a normal EEG and no CSF pleocytosis, which emphasizes the importance of NMDA receptor antibody testing in CSF for accurate diagnosis.