Age / Sex : 26 / M

Chief complaint :

Numbness and tingling sensation of both hands and soles for 1 month

Discussion

Answer:  

 Subacute combined degeneration of the spinal cord (complication of vitamin B12 deficiency) due to nitrous oxide abuse

Findings:

 T2-weighted sagittal image shows increased signal intensity (SI) in the cervical spinal cord from C2 to C5 levels
  T2-weighted axial image shows that the abnormal SI involves in the posterior column of the cervical spinal cord.
  T1-weighted contrast-enhanced axial image shows no abnormal enhancement

Differential Diagnosis:

 Multiple sclerosis

Neuromyelitis optica

Acute idiopathic transverse myelitis

Acute disseminated encephalomyelitis (ADEM)

Discussion:

• Nitrous oxide (N2O):
  
  
  
  • inhalational anesthetic agent, food aerosol propellant (whipped cream), engine accelerant, colorless, non-flammable gas with a slightly sweet taste, euphoric and hysterical effects, also called “laughing gas”, more than 10 N2O bulbs/day has a potential to result in significant neurological complications
  
  
  • irreversibly oxidising the cobalt ion of cobalamin (Vit B12) à inhibit methylation of myelin sheath phospholipids à demyelination of the nervous system involving the spinal cord and sometimes peripheral neuropathy and optic atrophy à subacute combined degeneration through inactivation of the Vit B12 metabolism
  
  
  
  


• MRI findings of subacute combined degeneration:
  
  
  
  • bilateral symmetric T2 high SI of dorsal columns and lateral cortical spinal tracts, lower cervical and upper thoracic spinal cord level, no abnormality on the pre- or postcontrast T1-WI
  
  
  
  


• Nitrous oxide (N2O) Toxicity:
  
  
  
  • slowing of motor conduction velocities in peripheral nerve conduction studies, ↓ serum vitamin B12 (normal in up to 30% ), ↑ methylmalonic acid, Homocysteine
  
  
  
  


• Nitrous oxide (N2O) Management
  
  
  
  • vitamin B12 injections and physiotherapy
  
  
  
  

References:

• Peter J Pema, Holli A Horak, and Robert H. Wyatt. Myelopathy Caused by Nitrous Oxide Toxicity. AJNR Am J Neuroradiol 19:894 –896, May 1998


• Hui Mei Cheng, Jae Hong Park, David Hernstadt. Subacute combined degeneration of the spinal cord following recreational nitrous oxide use. Cheng HM, et al. BMJ Case Rep 2013.


• Dustin Anderson, Grayson Beecher, Rene van Dijk, Mohammed Hussain, Zaeem Siddiqi, Fang Ba. Subacute Combined Degeneration from Nitrous Oxide Abuse in a Patient with Pernicious Anemia. Can J Neurol Sci. 2018; 45: 334-335