Anti-N-Methyl-D-Aspartate Receptor (Anti-NMDAR) Encephalitis in Small Cell Lung Cancer: A Case Report.

Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis is an autoimmune encephalitis characterized by psychiatric and neurological symptoms. It often presents as a paraneoplastic manifestation and is rarely associated with small cell lung cancer. While treatment usually involves immunotherapy and treatment of underlying malignancy, the patient's condition can complicate treatment decisions. A 66-year-old man presented to the emergency department with a chief complaint of fever and impaired consciousness. Tests revealed anti-NMDAR encephalitis and small cell lung cancer. Despite immunotherapy, including steroids, intravenous immunoglobulin, and rituximab, chemotherapy was not possible due to the patient's poor condition. Immunotherapy treatment was continued, but there was no improvement in his state of consciousness, and death was confirmed on the 101st day of hospitalization. Anti-NMDAR encephalitis caused by small cell carcinoma is treated with immunotherapy and cancer therapy; only immunotherapy is not enough.