1245 - Subacute Combined Degeneration of the Spinal Cord following Chronic Nitrous Oxide Use

Case Diagnosis: Subacute Combined Degeneration

Case Description: This is a 26-year-old male with history of depression, alcohol use, and nitrous oxide (NO) use who presented with bilateral lower extremity pain and weakness, and upper and lower extremity paresthesias. The patient reported consumption of 300 NO capsules/day for the last 4 months. On exam, the patient had bilateral lower extremity weakness, with reduced vibratory sensation and proprioception at the knuckles and absent below the waist bilaterally. He demonstrated ataxia with finger-nose and heel-shin testing. Vitamin B12 level was 93 pg/ml. A thoracic spine MRI demonstrated dorsal central cord hyperintense signals from the lower cervical spine through T6, representing thoracic spine cord myelopathy. Following vitamin B12 supplementation, the patient reported improved sensation, but had persistent gait ataxia, intermittent foot numbness, and bilateral foot drop requiring AFOs while in rehab.

Discussions: NO has historically been used for its analgesic and anesthetic properties but has become popular recreationally due to its rapid euphoric effects. In the 2021 Global Drug Survey Report, 22.5% of respondents reported NO use within their lifetime and 9.7% within the last year. Studies demonstrate that chronic NO use leads to inactivation of vitamin B12 via oxidation of cobalt, causing functional defects in vitamin B12 as a cofactor for methionine synthetase and the catabolism of homocysteine and methylmalonic acid. Vitamin B12 deficiency can result in neuronal demyelination, disruption of DNA synthesis, inhibition of NMDA receptors, and stimulation of dopaminergic and noradrenergic neurons. We present a patient with history of chronic NO use with symptoms of pain, weakness, and paresthesias with moderate improvement in sensation following vitamin B12 supplementation.

Conclusions: Chronic NO use causes vitamin B12 inactivation through its interaction with enzymatic cofactors, which can lead to myeloneuropathy. This case highlights the need for further investigation into how NO may result in permanent SCI despite vitamin B12 supplementation.