Science News: Nitrous Oxide-Induced Myeloneuropathy

Submitted by: Shan Chen, MD
Edited by: Francisco Gomez, MD

Swart G, Blair C, Lu Z, et al. Nitrous oxide-induced myeloneuropathy. Eur J Neurol. 2021;28(12):3938-3944. doi:10.1111/ene.15077

Summary: Nitrous oxide (NO, also known as laughing gas, balloons, whippets) abuse is increasingly recognized as an issue worldwide. Prolonged NO misuse inactivates vitamin B12, causing combined subacute degeneration.
 
The authors studied a cohort of 20 patients with NO misuse. The average patient age was 24 years and mean canister consumption was 148 per day for 9 months. Common presentation included sensory symptoms with paresthesias and gait unsteadiness. In severe cases, patients were bedbound (7 out of 20). Mean serum B12 was normal (258 pmol/L, normal range [NR] = 140-750) as was active B12 (87 pmol/L, normal > 35).
 
In contrast, mean serum homocysteine was markedly high (51 μmol/L, NR = 5-15). Spinal magnetic resonance imaging (MRI) showed characteristic dorsal column T2 hyperintensities in all 20 patients. Nerve conduction studies showed a predominantly axonal sensorimotor neuropathy (n = 5). Patients were treated with intramuscular vitamin B12, with varying functional recovery. Three of the seven patients who were bedbound at presentation were able to walk again with aid at discharge. Most of the eight patients they had followed had persistent paresthesias and/or sensory ataxia. Mobility scores at admission and discharge were not significantly correlated with the serum total and active B12 levels or cumulative nitrous oxide use. There were also no significant trends between serum active B12 level and cumulative nitrous oxide use (Spearman rho = -0.331, p = 0.195).
 
Comments: NO misuse is an increasingly prevalent issue worldwide. It is cheap, legal, and easily accessible via internet purchase. Recognizing NO induced myeloneuropathy has become more important. NO misuse can cause a severe but potentially reversible subacute myeloneuropathy. Most importantly, vitamin B12 serum level could be normal. Homocysteine level can be elevated. Further imaging and NCS testing are beneficial.
 
This is an excellent small case series on 20 patients with NO abuse. The data presented, although not complete due to loss of follow-up, are still highly informative.
 
Article of Similar Interest:
Redmond J, Cruse B, Kiers L. Nitrous oxide-induced neurological disorders - an increasing public health concern. Intern Med J. 2021 Sep 27. doi: 10.1111/imj.15544. Epub ahead of print. PMID: 34569693.