Disclosures: Arielle Berkowitz, DO: No financial relationships or conflicts of interest

Case Diagnosis: A 28-year-old woman with three months of daily nitrous oxide inhalation.

Case Description: A 28-year-old woman with anxiety, depression, and ADHD presented with several weeks of ascending paresthesias, frequent falls, and difficulty ambulating.  She reported inhaling nitrous oxide (NO) up to 300 canisters daily over the preceding three months.  Neurological examination revealed allodynia, reduced vibratory sensation and proprioception, positive Romberg, and unsteady gait. Cervical spine MRI revealed longitudinally extensive C2-C7 dorsal column signal abnormality consistent with subacute combined degeneration of the spinal cord (SCD). Serum vitamin B12 was 274, homocysteine 41 and methylmalonic acid 7.01.

Setting: Acute Inpatient RehabilitationAssessment/

Results: Patient was transferred to acute inpatient rehabilitation for physical and occupational therapy focused on improving gait and ADL retraining. She received vitamin B12 1000 mcg intramuscularly daily for 7 days followed by 1000 mcg weekly.  Her functional status improved to independent/modified independent with most activities and supervision for higher level balance skills. Repeat MRI was unchanged.  She was discharged home on oral vitamin B12 2000 mcg daily.

Discussion: B12 deficiency secondary to NO inhalation is an uncommon but potentially reversible cause of SCD. NO inactivates vitamin B12 via oxidation of the cobalt atom, leading to impaired methylation of myelin protein with resultant demyelinating lesions appearing initially in the dorsal columns of the spinal cord.  Serum vitamin B12 may be decreased or normal; homocysteine and methylmalonic acid are often elevated and can aid in diagnosis.  Although typically slow and often incomplete, neurologic recovery can occur in 2-3 weeks with oral/intramuscular vitamin B12 supplementation.

Conclusion: The dorsal columns are critical for proprioception, vibration, and temperature sensation. It is important to be aware of the relationship between NO inhalation and vitamin B12 deficiency to facilitate accurate diagnosis and prompt treatment of this potentially reversible cause of dorsal column dysfunction.

Level of Evidence: Level V

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/subacute-combined-degeneration-of-the-spinal-cord-secondary-to-b12-deficiency-in-the-setting-of-nitrous-oxide-inhalation-a-case-report/