Nitrous oxide abuse induced subacute combined degeneration despite patient initiated B12 supplementation

Introduction: Nitrous oxide (N₂O) is a commonly used inhaled anesthetic that is legal to purchase as a food additive and is popular as a recreational euphoric drug. Abuse causes a functional B12 deficiency, leading to clinical features and imaging consistent with subacute combined spinal cord degeneration (SCD). Cases: Poison Center medical records from four patients are reviewed in this series. Four patients presented with lower extremity weakness, paresthesias and gait abnormalities in the setting of chronic N₂O abuse. Each reported using 50–150 N₂O cartridges (“whippets”) almost daily for months to years, and reported supplementing with oral B12 at the recommendation of other users and online forums. None reported prior B12 deficiency or dietary restrictions, and none exhibited hematologic abnormalities. Results: All patients had clinical signs of neurotoxicity including weakness and ataxia. Additionally, all had elevated methylmalonic acid and homocysteine concentrations with normal B12 indicating a functional B12 deficiency. Three had imaging consistent with SCD despite home supplementation The MRI in the fourth case was inconclusive due to movement artifact. Conclusion: We report four cases of subacute combined degeneration induced by recreational nitrous oxide abuse despite self-administered vitamin B12 supplementation.