Anti-N-Methyl-D-Aspartate (Anti-NMDA) Receptor Encephalitis as the Initial Presentation of Small Cell Carcinoma of the Lung in a Middle-Aged Man

This case report describes a previously healthy 55 year-old man with unremarkable family and medical history presenting with Cotard delusion, unintentional weight loss, and psychomotor agitation requiring sedation. Testing revealed CSF leukocytosis and erythrocytosis, leading to a preliminary diagnosis of viral herpes encephalitis. As the patient continued to deteriorate, anti-NMDA receptor antibodies were detected in the CSF, yielding a diagnosis of anti-NMDA receptor encephalitis. Chest CT and left hilar lymph node biopsy confirmed small cell carcinoma of the lung. Anti-NMDA receptor encephalitis is a rare paraneoplastic or autoimmune syndrome that may be the sign of an underlying malignancy, as demonstrated in this extraordinarily rare presentation. Caretakers should have a high degree of suspicion for this syndrome in patients with no neurologic or psychiatric history presenting with acute mental status changes.