A Case of N-Methyl-D-Aspartate (NMDA) Autoimmune Encephalitis in a 34-Year-Old Man Thought to Have Schizophrenia.

Background: N-methyl-d-aspartate (NMDA) autoantibody encephalitis is a rare autoimmune condition affecting approximately 1.5 per million people per year [1]. It predominantly occurs in young women and is often associated with tumors, particularly teratomas [3]. The diagnosis is aided by testing cerebrospinal fluid (CSF) or serum for NMDA receptor antibodies along with careful evaluation of symptoms. Misdiagnosis is common, as its symptoms can mimic other more prevalent conditions, such as upper respiratory illnesses or psychiatric disorders like acute psychosis or schizophrenia. Case report: We present the case of a 34-year-old man who was initially incarcerated and subsequently developed decreased communication and mild agitation over several days, leading to his transfer to a psychiatric institute with a presumed diagnosis of schizophrenia. As his encephalopathy worsened over weeks, he exhibited catatonic symptoms and was referred to our facility for further evaluation after an unrevealing workup, including an initial lumbar puncture.Upon re-evaluation, a lumbar puncture was repeated with an autoimmune panel, returning positive for anti-NMDA antibodies, confirming the diagnosis. The patient was initially treated with steroids and plasma exchange, resulting in minimal improvement. He later received intravenous immunoglobulin (IVIG) and concomitant rituximab, leading to some functional improvement to a non-verbal but alert state. Conclusion: This case highlights the importance of considering rare autoimmune encephalitis' in patients presenting with worsening encephalopathy in the setting of a new psychiatric diagnosis, despite its rare nature.