Pattern-reversal visual evoked potential in a case of nitrous oxide abuse and recovery

Neurologic, psychiatric, and other medical manifestations of nitrous oxide abuse: A systematic review of the case literature

BACKGROUND/OBJECTIVES

Nitrous oxide (N2 O) is known to have abuse potential, although debate regarding the toxic effects of such abuse continues. Our objective was to review the case literature and present the neurologic, psychiatric and medical consequences of N2 O abuse.

METHODS

A systematic literature review was completed for case reports using keywords "nitrous oxide" with "abuse/abusing" or "misuse/misusing" or "overuse/overusing" or "addiction." Non-English-language cases and cases not involving direct toxic effects of N2 O were excluded as were commentaries or personal essays. Clinical presentation, frequency of N2 O abuse, laboratory studies, imaging, ancillary tests, treatments and outcomes were collected from case reports.

RESULTS

Our review returned 335 Pubmed, 204 Web of Science, 73 PsycINFO, 6 CINAHL, 55 EMBASE and 0 Grey Literature results, and after exclusion and removal of duplicates, 91 individual cases across 77 publications were included. There were also 11 publications reporting 29 cases of death related to N2 O abuse. The majority of cases (N = 72) reported neurologic sequelae including myeloneuropathy and subacute combined degeneration, commonly (N = 39) with neuroimaging changes. Psychiatric (N = 11) effects included psychosis while other medical effects (N = 8) included pneumomediastinum and frostbite. Across all cases N2 O abuse was correlated with low or low-normal Vitamin B12 (cyanocobalamin) levels (N = 52) and occasionally elevated homocysteine and methylmalonic acid.

CONCLUSIONS/SCIENTIFIC SIGNIFICANCE

N2 O abuse represents a significant problem because of the difficulty involved with identification and the toxicity related to chronic abuse including possible death. Health professionals should be aware of the toxic effects of N2 O and be able to identify potential N2 O abuse. (Am J Addict 2016;25:358-369).

Neurotoxicity of nitrous oxide: multimodal evoked potentials in an abuser

INTRODUCTION

Nitrous oxide (N2O) damages the nervous system of chronic abusers. Multimodal evoked potentials (EPs) can help document the electrophysiological abnormalities of N2O abusers and its distribution in the nervous system.

CASE REPORT

A 41-year-old male N2O abuser had used N2O (4-5 cans/per day, about 2000 ml/can) for more than 10 years. He complained of progressive motor clumsiness and distal paresthesia in the four limbs. Abnormal laboratory tests were megaloblastic red blood cells (102.3 fL, normal 80-94 fL) and serum vitamin B12 concentration of 143 pg/nL (normal 160-970 pg/nL). An MR image did not show significant findings in the brain but demonstrated conspicuous changes in the posterior and lateral columns at the C2-C7 level, in accordance with the anatomical lesions of the subacute combined degeneration of the spinal cord. In addition to sensori-motor axonal polyneuropathy, multimodal EPs showed abnormal visual EPs with prolonged peak latencies of P100, abnormal brainstem auditory EPs characterized by delayed wave V and difficulty in the recognition of waves I and III, abnormal somatosensory EPs with significant decreased peak amplitudes of cortical potentials bilaterally, and abnormal motor EPs to transcranial magnetic stimulation with prolonged central motor conduction time.

CONCLUSION

Our studies document electrophysiological abnormalities that may be attributed to N2O and indicate that N2O may indirectly involve multiple levels of the nervous system.

Automated evoked potential monitoring

We have developed a computer system for use in the operating room and intensive care unit for the automated acquisition and classification of flash evoked potentials. The project goals were to: (1) acquire evoked potentials without user intervention; (2) recognize, label, and trend important parameters; and (3) alarm if parameters deviate too far from normal. The system consists of a Nicolet Pathfinder, programmed for periodic flash visual evoked potential acquisition and a personal computer for analysis. Analysis software utilizes the C+ +language. The system has been tested on sixteen cases, determinations of specific waveforms were validated ex post facto by two experts. Three parameters in each of three channels were correctly recognized in more than 87% of all waveforms acquired. No signals at all were obtained in only 0.8% of all samples.