Nonconvulsive status epilepticus associated with leptomeningeal carcinomatosis and positive SOX1 antibodies

Background Nonconvulsive status epilepticus (NCSE) is a disorder with varying prognoses depending on the underlying etiology. It is increasingly recognized as a cause of altered mental status but is difficult to diagnose without continuous electroencephalogram (EEG) monitoring. Case Report A 75-year-old woman visited our emergency department with acute altered mental status. A cerebrospinal fluid study showed meningeal carcinomatosis. The EEG showed NCSE. Brain magnetic resonance imaging showed diffuse meningeal enhancement around the brain stem. There were no other masses except suspected primary lung cancer on chest computed tomography. However, no malignant cells were detected in a bronchial washing. Levels of carbohydrate antigen 19-9 (CA19-9), CA125, and CA 15-3 were elevated. Autoimmune antibodies were all negative except for SOX1. The patient was unresponsive to first intrathecal chemotherapy and expired two days later. Conclusion This is a case report of NCSE caused by paraneoplastic autoimmune encephalitis associated with SOX1 antibodies.