Subacute combined degeneration from nitrous oxide abuse.

Nitrous oxide is an anesthetic medication which can also be recreationally abused in the form of whippet canisters. Its prolonged abuse can interfere with Vitamin B12 metabolism and lead to its functional deficiency. We report a case of a 30-year-old male who presented with generalized weakness and was found to have subacute combined degeneration (SCD) of the spinal cord. His laboratory workup showed low Vitamin B12 with elevated homocysteine and methylmalonic Co-A levels, and further questioning revealed prolonged nitrous oxide abuse. Nitrous oxide causes functional inactivation of methylcobalamin by rendering it unable to function as a coenzyme for methionine synthase enzyme. This leads to the decreased production of methionine and subsequent production of myelin. This case describes nitrous oxide abuse as an important etiology to be considered in patients presenting with weakness and myeloneuropathy and describes important imaging findings.