Bilateral pulmonary embolism in anti-NMDA receptor encephalitis presenting as acute psychosis.

BACKGROUND: Anti-N-methyl-D-aspartate (NMDA) receptor encephalitis is an autoimmune disorder that frequently presents with prominent psychiatric manifestations, often leading to misdiagnosis as a primary psychiatric illness. Early recognition is critical, as timely immunotherapy significantly improves outcomes. CASE PRESENTATION: A 26-year-old previously healthy man presented with acute psychosis following significant emotional stress and first-time marijuana use 3 days earlier. Initially diagnosed with brief psychotic disorder, he developed catatonia and fever. Cerebral spinal fluid (CSF) and serum anti-NMDA receptor antibodies confirmed the diagnosis. His course was complicated by bilateral pulmonary emboli and drug-induced liver injury. Treatment with intravenous immunoglobulin (IVIG) and high-dose corticosteroids resulted in marked improvement. Malignancy work-up was negative. CONCLUSION: This case underscores the importance of considering autoimmune encephalitis in young patients presenting with new-onset psychosis, in the apparent absence of malignancy. A high index of suspicion and early CSF evaluation can prevent diagnostic delay and improve patient outcomes.