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

Background: Whilst 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 (NO) have been reported. Here we set out to raise awareness of subacute degeneration of the spinal cord arising from recreational NO use so that formal surveillance programs and public health interventions can be designed.

Methods: Case 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.

Results: Sensory 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 T weighted sequences. Serum B levels may be normal because subacute degeneration of the spinal cord in this situation is triggered by functional rather than absolute B deficiency.

Discussion: A 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 NO. 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.