Protracted encephalopathy and subacute combined degeneration associated with chronic nitrous oxide use: a case report.

Nitrous oxide is a dissociative hallucinogen that is increasingly used recreationally, in part due to its widespread availability. Its use is known to cause subacute combined degeneration via inactivation of vitamin B12; it may also result in acute delirium and chronic progressive encephalopathy. Though current practice guidelines call for treatment of neurological sequelae of nitrous oxide use with vitamin B12 supplementation, a paucity of long-term outcome data limits our ability to guide extended courses of treatment. In this report, we discuss a case of protracted encephalopathy associated with nitrous oxide use. We track the response to vitamin B12 supplementation in the hospital setting using the Mini-Mental Status Exam to assess the severity and improvement of cognitive impairment. We also review the patient's comorbid medical and psychiatric conditions, which complicate diagnosis and treatment planning in this patient population.