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

Abstract

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.

<p>Clinical, Electrophysiological and Radiological Features of Nitrous Oxide-Induced Neurological Disorders</p>

“…6 Multiple case studies have reported that the neurological and psychiatrical disorders, such as subacute combined degeneration, myelopathy, demyelinating polyneuropathy and emotional disorders, are related to N 2 O abuse. [7][8][9][10] There have even been deaths related to N 2 O inhalation. 11 Considering about the lack of awareness of N 2 O-abusing toxicity, we conducted a clinical study, which included a comprehensive and updated review of N 2 O abuse-induced neurological disorders.…”

Vitamin B12status in health and disease: a critical review. Diagnosis of deficiency and insufficiency – clinical and laboratory pitfalls

“…Therefore, biochemically, highly elevated tHcy is seen first in patients who abuse N 2 O, followed by a slow decrease in serum B 12 and holoTC, as well as slight elevations in MMA. Serum B 12 is often normal at presentation [218,219], which may lead to an incorrect differential diagnosis. It has been also suggested that inactive Me-Cbl is converted to Ado-Cbl [216].…”

Subacute Combined Degeneration from Nitrous Oxide Abuse

“…Patients presenting with N 2 O‐induced SCD typically have a history of regular N 2 O abuse for several months. Neurological symptoms most commonly include paresthesia of the limbs, diminished proprioception and vibration sensation, ataxia, and later muscle weakness . Autonomic dysfunction and cognitive impairment may also be present .…”

“…Patients may have normal to low vitamin B12 levels, but methylmalonic acid and/or homocysteine levels are typically elevated and provide a more effective method to diagnose or screen for functional B12 deficiency . Inactivation of vitamin B12 ultimately leads to swelling of myelin sheaths and patchy myelopathic spongy vacuolation with demyelination, axonal swelling, and eventually axonal death …”

“…Treatment includes cessation of N 2 O use, prompt intramuscular vitamin B12 supplementation, and physical therapy. The prognosis is variable and may be slow with partial to full recovery . Factors associated with favorable prognosis include younger age, less severe neurological deficits, less extensive spinal cord lesions on magnetic resonance imaging (MRI), absence of anemia, and early treatment …”