Subacute Combined Degeneration Caused by Nitrous Oxide Intoxication: A Report of Two Cases

We report two cases of subacute combined degeneration (SCD) caused by nitrous oxide (N2O) gas intoxication, which is rarely reported in Korea. Two patients recreationally inhaled N2O gas daily for several months. They presented with paresthesia of limbs, voiding difficulty, and gait disturbance. The initial vitamin B12 levels were normal or decreased, but homocysteine levels of the two patients were increased. Magnetic resonance imaging of the cervical spine showed T2-weighted hyperintensity in the bilateral dorsal columns of the cervical spinal cord. Electromyography and somatosensory evoked potential tests for both patients suggested posterior column lesion of the spinal cord combined with sensorimotor polyneuropathy. According to these findings, we concluded that the two patients had SCD. The patient's symptoms partially improved after cessation of N2O gas inhalation and the receiving of vitamin B12 supplementation therapy. As the incidence of recreational N2O gas inhalation is increasing in Korea, physicians must be alert to the N2O induced SCD in patients presenting with progressive myelopathy.