Clinical Case DiscussionsAnti-NMDA Receptor Encephalitis Masquerades as Psychosis: A Case ReportGiri, Yam R. MD; Korie, Ijendu MD; Hashmi, Seema MD; Parrill, Allison MD; Ayed, Nisrin MDAuthor Information GIRI, KORIE, and HASHMI: Department of Psychiatry, Nassau University Medical Center, East Meadow, NY PARRILL: American University of the Caribbean School of Medicine, Cupecoy, Saint Martin AYED: Jordan University of Science and Technology, Irbid, Jordan Y.R.G. and I.K. contributed equally to writing, reviewing, and editing this manuscript. A.P., S.H., and N.A. contributed by literature search, reviewing, and editing the manuscript. The authors declare no conflicts of interest. Please send correspondence to: Yam R. Giri, MD, 2201 Hempstead Turnpike, East Meadow, NY 11554 (e-mails: [email protected]; [email protected]). Journal of Psychiatric Practice: January 2022 - Volume 28 - Issue 1 - p 72-77 doi: 10.1097/PRA.0000000000000603 Buy Metrics Abstract A 28-year-old male patient with an unclear history of psychosis was admitted to the inpatient psychiatric unit. He presented with auditory hallucinations, agitation, and bizarre and disorganized behavior. He was treated with antipsychotic medications without improvement. Magnetic resonance imaging of the brain showed hyperintensities throughout the brain parenchyma. Investigations for infectious, metabolic, autoimmune, and malignant etiologies were negative. Anti–N-methyl-D-aspartate (NMDA) receptor encephalitis was suspected. Cerebrospinal fluid (CSF) and serum NMDA receptor antibody testing were performed. Both tests were positive, confirming anti-NMDA receptor encephalitis. The patient was treated with intravenous immunoglobulin and methylprednisolone, which resulted in the resolution of his psychosis. In the case of unexplained psychosis associated with seizures, early screening using serum and CSF testing for anti-NMDA receptor antibodies and brain magnetic resonance imaging may be an important diagnostic tool for detecting anti-NMDA receptor encephalitis. Detailed investigations of CSF and serum should be performed to rule out infectious, metabolic, and autoimmune causes. Imaging studies should also be performed to identify any tumors such as a teratoma. This approach may help identify patients with anti-NMDA receptor encephalitis masquerading as psychosis. Early diagnosis and treatment including intravenous steroids, immunosuppressants, plasmapheresis, and removal of any teratoma if present in patients with anti-NMDA receptor encephalitis can improve the overall outcome. Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.