Clinical Reasoning: a 20-Year-old Woman with Coma and Quadriplegia.

Dear editor,Subacute combined degeneration（SCD） of the spinal cord, which is mainly caused by vitamin B12 deficiency, reveals damage in posterior and lateral columns and peripheral nerves. The CNS and cranial nerves are rarely involved except in children. [1,2] Spinal cord MRI abnormal long T1 and T2 signs in the posterior funiculus has specificity for the diagnosis. [3] There have been many case reports about SCD induced by nitrous oxide anaesthesia or entertainment.