442 - Polyneuropathy Secondary to Nitrous Oxide Abuse and Functional Vitamin B12 Deficiency: A Case Report

Case Diagnosis: 23-year-old male with a drug-induced polyneuropathy secondary to chronic nitrous oxide misuse and subsequent functional B12 deficiency.

Case Description: A 23-year-old male presented to the emergency department with a four week history of bilateral foot paresthesia that ascended to the level of his umbilicus over the prior two days. His medical history was significant for habitual marijuana, tobacco, and nitrous oxide inhalation over the previous year with an increase in N2O abuse to 400 times per week in the last three months. He endorsed balance difficulty, saddle anesthesia, and straining with urination/defecation. Neurologic exam revealed a sensory ataxia with decreased vibratory sensation, proprioception, and two-point discrimination from the level of the umbilicus to the toes. Labs revealed B12 deficiency, hyperbilirubinemia, and significantly elevated homocysteine and methylmalonic acid. The patient was diagnosed with a subacute combined degeneration secondary to a nitrous oxide-induced functional B12 deficiency. He was discharged from the ED with follow-up appointments with neurology and psychiatry and prescriptions for intramuscular B12 injections, physiotherapy, and incentive spirometry.

Discussions: B12 deficiency typically occurs due to malabsorption or dietary insufficiency. This case report highlights another mechanism in which nitrous oxide, inhaled from household whipped cream canisters, binds and inactivates B12 leading to polyneuropathy. This patient received an outpatient C-spine MRI and EMG that were consistent with a diagnosis of SCD. After three months of treatment, his gait had normalized, he had slight sway with Romberg’s test, paresthesia was isolated below the mid-shin, and proprioception was intact.

Conclusions: This unique case of SCD due to a socio-behavioral problem resulted in nearly complete recovery of function after only 3 months of physiotherapy and intramuscular B12 injections, serving as a strong predictor for recovery in future cases with a similar presentation.