Unveiled: A Case of N-Methyl-D-Aspartate Receptor Antibody Encephalitis With Delayed Diagnosis of Ovarian Teratoma

N-methyl-D-aspartate receptor (NMDAR) antibody encephalitis is an autoimmune syndrome with potentially fatal sequelae causing profound dysregulation of neurotransmission. Patients most often present with a constellation of neuropsychiatric signs and symptoms, including behavioral changes, motor disturbances, and seizures. Frequently, the development of anti-NMDAR antibodies has been linked to specific malignancies, although the exact event that triggers the production of these antibodies remains unknown. We present a case of a 25-year-old female who came into the emergency room with behavioral changes and fever. The patient had non-convulsive seizures, catatonia, and orofacial dyskinesias during the course of the admission and was treated as a case of autoimmune anti-NMDAR encephalitis. Cranial and abdominal MRI with contrast initially showed negative results, while the serum and cerebrospinal fluid studies were positive for anti-NMDAR antibodies. The patient was noted to have significant clinical improvement after being treated with high-dose intravenous steroid therapy followed by intravenous immunoglobulin (IVIg) and rituximab infusion. She was discharged stable with the resolution of neurologic symptoms four months after the diagnosis. On follow-up with her neurologist two years later, an abdominal CT scan was done and showed mature cystic teratoma. This is one of the few documented cases of anti-NMDAR encephalitis with a good response to medical treatment but had a delayed diagnosis of ovarian teratoma seen on surveillance work-up years after the diagnosis. A high index of suspicion is warranted for the diagnosis, and treatment should be started early as soon as there is clinical suspicion of the disease. Also, surveillance pelvic or abdominal imaging is important in patients who have negative initial screening but have high risks for teratomas.