Nitrous oxide-induced subacute combined degeneration of the cord: diagnosis and treatment.

Recreational use of nitrous oxide (N 2 O) has increased rapidly in recent years and is now the second most commonly used recreational drug among young people in the UK. There has been a corresponding rise in cases of nitrous oxide-induced subacute combined degeneration of the cord (N 2 O-SACD), a pattern of myeloneuropathy usually associated with severe vitamin B 12 deficiency. This can cause serious and permanent disability in young people but, if recognised early, may be effectively treated. All neurologists should be aware of N 2 O-SACD and its treatment; however, there are currently no agreed guidelines. Based on our experience in East London, an area of high N 2 O use, we provide practical advice on its recognition, investigation and treatment.