No laughing matter: subacute degeneration of the spinal cord due to nitrous oxide inhalation

Abstract

BackgroundWhilst the dangers of ‘legal highs’ have been widely publicised in the media, very few cases of the neurological syndrome associated with the inhalation of nitrous oxide (N2O) have been reported. Here we set out to raise awareness of subacute degeneration of the spinal cord arising from recreational N2O use so that formal surveillance programs and public health interventions can be designed.MethodsCase series documenting the clinical and investigational features of ten consecutive cases of subacute degeneration of the spinal cord presenting to a hospital with a tertiary neurosciences service in East London.ResultsSensory disturbance in the lower (± upper) limbs was the commonest presenting feature, along with gait abnormalities and sensory ataxia. MRI imaging of the spine showed the characteristic features of dorsal column hyperintensity on T2 weighted sequences. Serum B12 levels may be normal because subacute degeneration of the spinal cord in this situation is triggered by functional rather than absolute B12 deficiency.DiscussionA high index of suspicion is required to prompt appropriate investigation, make the diagnosis and commence treatment early. This is the largest reported series of patients with subacute degeneration of the spinal cord induced by recreational use of N2O. However, the number of patients admitted to hospital likely represents the ‘tip of the iceberg’, with many less severe presentations remaining undetected. After raising awareness, attention should focus on measuring the extent of the problem, the groups affected, and devising ways to prevent potentially long-term neurological damage.

Subacute progressive sensorimotor symptoms

“…SCDC has been reported after N 2 O use ranging from 75 to 2000 cannisters a week1 (typically 8 g N 2 O per cannister) and may emerge after just two weeks’ intense use 2…”

“…The treatment of SCDC is 1 mg intramuscular hydroxocobalamin on alternate days until there is no further improvement, followed by monthly injections 12. N 2 O abstinence is crucial 3…”

“…One case series reports persistent sensory symptoms in half of all patients with N 2 O mediated myeloneuropathy following treatment 1. Other case series have reported outcomes ranging from complete recovery to permanent paraparesis 24…”

“…Both recreational and medicinal use of N 2 O can result in peripheral neuropathy, myelopathy, or both13…”

Laughter isn’t always the best medicine

“…Adolescents and young adults presenting with the neurological complications of repeated N 2 O use are seen regularly in east London emergency departments 1. Greater awareness of this emerging public health problem is needed.…”