Subacute Combined Degeneration and Acute Pulmonary Embolism Caused by Nitrous Oxide–Induced Vitamin B12 Deficiency

Nitrous oxide (NO) misuse is an underrecognized cause of vitamin B12 deficiency. Patients may present with paresthesia, ataxia, cognitive and behavioral changes, macrocytic anemia, and thromboembolism. We describe a 50-year-old man with heavy NO use who presented with a 1-month history of paresthesia, unsteady gait, and neurocognitive decline and a 2-day history of dyspnea. Laboratory studies revealed macrocytic anemia and low vitamin B12. After further investigation, the patient was diagnosed with subacute combined degeneration and acute pulmonary embolism secondary to NO-induced vitamin B12 deficiency. This case highlights the importance of early recognition and treatment with vitamin B12.