BACKGROUND: Over the last 3 years, there has been increasing awareness of nitrous oxide-induced myeloneuropathy, particularly among younger patients.

METHODS: We conducted a prospective and retrospective case series of patients presenting with nitrous oxide-associated myeloneuropathy to Tallaght University Hospital, between October 2022 and July 2024. Data were gathered regarding clinical presentation, investigations, and management of patients.

RESULTS: Eighteen patients were identified (mean age 20 years, 78% male). The most common presenting symptom was paraesthesia (15/18) followed by limb weakness (13/18) and gait impairment (8/18). All patients reported heavy use of inhaled nitrous oxide, with a minority (3/18) also reporting prophylactic use of B12 supplementation. Levels of vitamin B12 were low (4/18) or low normal (7/18) in the majority of patients. Homocysteine was raised in almost all patients in whom it was measured (14/16). Of those cases (16/18) where MR imaging of the spinal cord was available, T2 hyperintensity was noted in the cervical cord in 8/16 cases, and this extended to involve the thoracic cord in five of those cases. Of those who had nerve conduction studies performed (13/18), motor-predominant axonal neuropathy was the most common pattern seen.

CONCLUSION: Nitrous oxide abuse, and its neurological complications, continue to represent a significant public health concern, with associated burden on neurological services.