Spinal myoclonus in subacute combined degeneration caused by nitrous oxide intoxication.

A 26-year-old patient developed ascending weakness and paresthesias. Megaloblastic anemia and mildly reduced serum vitamin B12 (B12) concentration were noted. Myoclonus-like muscular contractions appeared over four extremities and in the trunk. She admitted inhaling nitrous oxide (N2O) as a euphoriant repeatedly at party. Following parenteral B12 administration, her neurological deficit promptly resolved. This case demonstrated the abuse of N2OI is an important cause of subacute combined degeneration (SCD) of the spinal cord. To our knowledge, this is the first report of involuntary movements in a patient with N2O intoxication. Although the mechanism remains unknown, involuntary movements similar to myoclonus should be considered as one of the extraordinary neurological manifestations of N2O intoxication.