title: Severe motor neuropathy or neuronopathy due to nitrous oxide toxicity after correction of vitamin B12 deficiency.
abstract: BACKGROUND
  Nitrous oxide (N2 O) toxicity can cause a sensory predominant myeloneuropathy identical to subacute combined degeneration caused by vitamin B12 deficiency. We describe a patient with a typical vitamin B12 deficiency syndrome after N2 O abuse who recovered and then developed a severe lower motor neuron syndrome following vitamin B12 correction. This suggests N2 O toxicity independent of functional vitamin B12 deficiency.
  
  
  METHODS
  Electrophysiological, serological, and clinical evaluations were undertaken in the evaluation of this patient.
  
  
  RESULTS
  A 22-year-old man abused N2 O and presented with a dorsal column syndrome with low vitamin B12 and high homocysteine serum levels. He recovered with treatment but presented later with profound motor axonal degeneration and normal vitamin B12, homocysteine, and methlymalonic acid levels.
  
  
  CONCLUSIONS
  This case illustrates that N2 O-associated severe motor neuropathy or neuronopathy can develop separately from typical vitamin B12 deficiency dorsal column myelopathy. This syndrome can present when functional measures of vitamin B12 deficiency have normalized.
authors.affiliation: Partners Neurology Residency, Brigham and Women's Hospital, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Morris
authors.forename: Karen
authors.initials: K
authors.lastname: Lynch
authors.forename: Steven A
authors.initials: SA
authors.lastname: Greenberg
mesh_terms: D006710:Homocysteine / Q000097:blood; D006801:Humans; D008297:Male; D016472:Motor Neuron Disease / Q000139:chemically induced*; D009609:Nitrous Oxide / Q000009:adverse effects*; D014805:Vitamin B 12 / Q000627:therapeutic use*; D014806:Vitamin B 12 Deficiency / Q000188:drug therapy*; D055815:Young Adult
chemical_list: D006710:Homocysteine; D009609:Nitrous Oxide; D014805:Vitamin B 12
keywords: B12 deficiency; cobalamin; motor neuropathy; myeloneuropathy; nitrous oxide; vitamin B12