SHM Converge Scientific Abstract ePoster Gallery-A Not-So-Laughing Matter: Inhaled Nitrous Causing Functional B12 Deficiency

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This case report highlights an important cause of vitamin B12 deficiency: inhaled nitrous oxide. A 27-year-old man with no prior medical history presented with paresthesias, numbness, and gait instability. Although his serum B12 was only borderline low at 215 pg/mL, his methylmalonic acid (MMA) was severely elevated and homocysteine was also high, confirming functional B12 deficiency. Cervical MRI showed dorsal column changes consistent with subacute combined degeneration.<br /><br />The patient initially had no obvious dietary or malabsorption cause for deficiency. Further history revealed chronic recreational nitrous oxide use for at least four weeks, about three times daily. Nitrous oxide can inactivate vitamin B12 by altering its cobalt ion, preventing normal transmethylation reactions even when measured B12 levels appear normal. This makes MMA testing especially important in patients with suspected nitrous oxide exposure.<br /><br />Treatment with intramuscular B12 replacement and stopping nitrous oxide led to symptom improvement. The report emphasizes that clinicians should consider nitrous oxide exposure in patients with unexplained neurologic symptoms or B12 deficiency, including cases where serum B12 is normal or borderline. It also reinforces diagnostic thresholds: B12 levels below 200 pg/mL confirm deficiency, while levels between 200 and 400 pg/mL should be interpreted with MMA testing.

Asset Subtitle

Joshua Lee

Meta Tag

Author List Joshua Lee, Maxwell Bressman MD

Category Clinical Vignettes

Concept Vitamin B12 Deficiency

Concept Serum Vitamin B12 Test

Concept Methylmalonic Acid

Concept Nitrous Oxide

Concept Functional Vitamin B12 Deficiency

Distinguished Non-Finalist

Presenter Organization New York Medical College (NYMC)

Presenting Author Joshua Lee

Track Adult

Keywords

vitamin B12 deficiency

nitrous oxide

methylmalonic acid

homocysteine

subacute combined degeneration

paresthesias

gait instability

recreational drug use

intramuscular B12 replacement

serum B12 borderline

Vitamin B12 Deficiency

Serum Vitamin B12 Test

Methylmalonic Acid

Nitrous Oxide

Functional Vitamin B12 Deficiency