BACKGROUND: Nitrous oxide (NO) is the second most common recreational drug used by 16- to 24-year-olds in the UK. Neurological symptoms can occur in some people that use NO recreationally, but most information comes from small case series.

METHODS: We describe 119 patients with NO-myeloneuropathy seen at NHS teaching hospitals in three of the UK's largest cities: London, Birmingham and Manchester. This work summarises the clinical and investigative findings in the largest case series to date.

RESULTS: Paraesthesia was the presenting complaint in 85% of cases, with the lower limbs more commonly affected than the upper limbs. Gait ataxia was common, and bladder and bowel disturbance were frequent additional symptoms. The mid-cervical region of the spinal cord (C3-C5) was most often affected on MRI T2-weighted imaging. The number of NO canisters consumed per week correlated with methylmalonic acid levels in the blood as a measure of functional B deficiency (rho (ρ)=0.44, p=0.04).

CONCLUSIONS: Preventable neurological harm from NO abuse is increasingly seen worldwide. Ease of access to canisters and larger cylinders of NO has led to an apparent rise in cases of NO-myeloneuropathy in several areas of the UK. Our results highlight the range of clinical manifestations in a large group of patients to improve awareness of risk, aid early recognition, and promote timely treatment.