An 18-year-old male patient developed numbness and fatigue in the limbs without any obvious causes,which aggravated to be unable to hold objects in hands,have difficulty in writing,standing and walking,and be easy to fall after 3 weeks.Laboratory tests showed his average erythrocyte volume 104 fl,homocysteine 89.1 μmol/L,vitamin B12 76 pmol/ml,and folic acid 14.9 nmol/L.MRI revealed image features of subacute combined degeneration of spinal cord.Nerve conduction velocity,action potential,and electromyography showed nerve damage signs.He was diagnosed with toxic myelopathy,subacute combined degeneration of spinal cord,and peripheral neuropathy.To find the cause of the disease,the doctor asked about the medical history repeatedly,and finally learned that the patient had taken nitrous oxide(N2O) for nearly 6 months(8-50 g/d).An Ⅳ injection of mecobalamine (0.5 mg,once daily),intramuscular injection of rat nerve growth factor (30 μg,once daily),as well as massage and acupuncture treatments were given.After 8 days,his average erythrocyte volume was 102 fl,homocysteine was 12.9 μmol/L,vitamin B12 was ＞ 1 500 pmol/ml,and folic acid was 14.1 nmol/L.After 3 weeks,numbness and fatigue of his upper limbs disappeared.After 3 months,the patient could walk up and down the hill and run.

An 18-year-old male patient developed numbness and fatigue in the limbs without any obvious causes,which aggravated to be unable to hold objects in hands,have difficulty in writing,standing and walking,and be easy to fall after 3 weeks.Laboratory tests showed his average erythrocyte volume 104 fl,homocysteine 89.1 μmol/L,vitamin B12 76 pmol/ml,and folic acid 14.9 nmol/L.MRI revealed image features of subacute combined degeneration of spinal cord.Nerve conduction velocity,action potential,and electromyography showed nerve damage signs.He was diagnosed with toxic myelopathy,subacute combined degeneration of spinal cord,and peripheral neuropathy.To find the cause of the disease,the doctor asked about the medical history repeatedly,and finally learned that the patient had taken nitrous oxide(N2O) for nearly 6 months(8-50 g/d).An Ⅳ injection of mecobalamine (0.5 mg,once daily),intramuscular injection of rat nerve growth factor (30 μg,once daily),as well as massage and acupuncture treatments were given.After 8 days,his average erythrocyte volume was 102 fl,homocysteine was 12.9 μmol/L,vitamin B12 was ＞ 1 500 pmol/ml,and folic acid was 14.1 nmol/L.After 3 weeks,numbness and fatigue of his upper limbs disappeared.After 3 months,the patient could walk up and down the hill and run.