SHM Converge Scientific Abstract ePoster Gallery-No Laughing Matter: Nitrous Oxide-Induced Subacute Combined Degeneration of the Spinal Cord

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A 34-year-old man with no significant past medical history presented with two weeks of progressive weakness, numbness, tingling, and intermittent shooting pain in his extremities. Exam showed distal and proximal weakness, loss of vibration and proprioception, and diminished sensation. Initial workup, including CBC, BMP, inflammatory markers, infectious and autoimmune studies, CT imaging, and lumbar puncture, was unrevealing. Brain and spine CT were normal, and MRI of the cervical spine showed symmetric dorsal column signal abnormality consistent with subacute combined degeneration (SCD) of the spinal cord.

Although his serum vitamin B12 level was only borderline low-normal, further testing revealed markedly elevated methylmalonic acid and homocysteine, confirming functional B12 deficiency. He later disclosed weekend recreational nitrous oxide use. The case was diagnosed as nitrous oxide-induced vitamin B12 inactivation causing SCD.

Nitrous oxide is a readily accessible recreational substance that can cause neurologic injury by impairing myelin synthesis through B12 inactivation. Symptoms of SCD include paresthesias, weakness, gait difficulty, and impaired vibration/proprioception. MRI classically shows an “inverted V” dorsal column hyperintensity. Because serum B12 can be normal in a substantial portion of cases, clinicians should check methylmalonic acid and homocysteine when suspicion remains high.

The patient was treated with daily cyanocobalamin injections and showed mild improvement. He was discharged with weekly B12 injections after declining acute rehabilitation. At three-week follow-up, he reported partial recovery, was walking independently, and had stopped nitrous oxide use.

This case emphasizes that nitrous oxide abuse may be overlooked and should be considered in patients with unexplained neurologic symptoms. Early recognition and prompt vitamin B12 replacement are important to limit harm and improve outcomes.

Asset Subtitle

Eric Chu

Meta Tag

Author List Eric Chu

Category Clinical Vignettes

Concept Nitrous Oxide Abuse

Concept Vitamin B12 Deficiency

Concept Subacute Combined Degeneration

Concept Vitamin B12 Replacement

Concept Dorsal Column Hyperintensity

Distinguished Non-Finalist

Presenter Organization Duke Raleigh Hospital

Presenting Author Eric Chu

Track Adult

Keywords

nitrous oxide abuse

vitamin B12 deficiency

subacute combined degeneration

methylmalonic acid

homocysteine

dorsal column hyperintensity

paresthesias

proprioception loss

cyanocobalamin treatment

neurologic injury

Nitrous Oxide Abuse

Vitamin B12 Deficiency

Subacute Combined Degeneration

Vitamin B12 Replacement

Dorsal Column Hyperintensity