PT  - JOURNAL ARTICLE
AU  - Adam Seed
AU  - Meesha Jogia
TI  - Lessons of the month: Nitrous oxide-induced functional vitamin B<sub>12</sub> deficiency causing subacute combined degeneration of the spinal cord
AID  - 10.7861/clinmed.2020-0072
DP  - 2020 May 01
TA  - Clinical Medicine
PG  - e7--e9
VI  - 20
IP  - 3
4099  - http://www.rcpjournals.org/content/20/3/e7.short
4100  - http://www.rcpjournals.org/content/20/3/e7.full
SO  - Clin Med2020 May 01; 20
AB  - We discuss the case of a 22-year-old man who presented with paraesthesia, reduced sensation and weakness in his limbs. Examination was in keeping with a myeloneuropathy. Initial investigations including vitamin B12 were unremarkable but magnetic resonance imaging of the spinal cord showed subacute combined degeneration. The patient reported heavy recreational use of nitrous oxide, which can cause functional deficiency of vitamin B12 with neurological sequelae. A diagnosis of functional vitamin B12 deficiency was made and confirmed by an elevated methylmalonic acid level. The patient received intramuscular hydroxocobalamin and made a good recovery following rehabilitation. Nitrous oxide use is prevalent and can have significant health effects. Many adverse effects are mediated through inactivation of vitamin B12 and can be detected by elevated homocysteine and methylmalonic acid levels. Early identification and prompt treatment are important to support neurological recovery.