Subacute combined degeneration of the spinal cord following nitrous oxide anesthesia: A systematic review of cases

Mechanisms and recent advances in the diagnosis and treatment of nitrous oxide-induced peripheral neuropathy: a narrative review

Under standard conditions, nitrous oxide (N2O) manifests as a colorless, odorless gas with a mildly sweet taste. The compound finds applications in various fields, including its use as an aerosol propellants, an accelerant in motor racing, and an anesthetic in surgical procedures and dentistry. Unfortunately, the recreational misuse of N2O has become prevalent among young individuals due to its euphoric and hallucinogenic effects. Compounding this issue is the fact that nitrous oxide can be easily obtained from over-the-counter household items, facilitating its non-medical use. The global community has witnessed a surge in the recreational utilization of nitrous oxide gas in recent years. Despite the widespread non-medical abuse of N2O, there remains inadequate understanding of the potential adverse effects resulting from exposure to it. This paper provides an overview of management findings, laboratory and electrodiagnostic characteristics, as well as clinical presentations associated with neurological disorders induced by nitrous oxide usage.

Neurological Manifestations Induced by Nitrous Oxide Abuse: A Case Series and Review of Literature

INTRODUCTION

Nitrous oxide (NO) abuse is increasing among young people. This can result in severe neurological disorders such as myelopathy and/or peripheral neuropathy. We report the clinical presentations, biological, radiologic and electrophysiological findings of 5 patients hospitalized with neurological symptoms consecutive to NO abuse. In addition, a literature review was conducted to describe the neurological characteristics and to identify factors associated with a poor recovery.

CASE REPORT

Among the 5 patients included, 2 had a myeloneuropathy, 2 had a sensorimotor neuropathy, and 1 had a normal spinal cord magnetic resonance imaging and electromyography despite neurological manifestations consistent with myeloneuropathy. After vitamin B 12 supplementation, recovery was reported in 4 patients, and 1 was lost to follow-up.From the literature review, 154 patients were included [94 males; median age 22 (19 to 26) y; NO exposure 9 (3 to 18) mo]. A myelopathy was identified in 116 patients (75%) and a peripheral neuropathy was documented in 89 patients (58%). Compared with patients who recovered, those with sequelae were more likely to have a motor deficit at presentation ( P <0.001), to use NO regularly ( P <0.001), to have a lower vitamin B 12 level ( P =0.04), and a higher concentration of homocysteine ( P =0.04). A less extensive myelopathy was more frequently found in the group with favorable outcomes ( P =0.002).

CONCLUSION

Neurological disorders caused by NO may be challenging with severe clinical patterns. We identified several factors associated with a poor recovery, to make clinicians aware of NO-induced neurotoxicity.

Metabolic and Toxic Myelopathies

OBJECTIVE

This article reviews the clinical presentation, diagnostic evaluation, and treatment of metabolic and toxic myelopathies resulting from nutritional deficiencies, environmental and dietary toxins, drugs of abuse, systemic medical illnesses, and oncologic treatments.

LATEST DEVELOPMENTS

Increased use of bariatric surgery for obesity has led to higher incidences of deficiencies in nutrients such as vitamin B12 and copper, which can cause subacute combined degeneration. Myelopathies secondary to dietary toxins including konzo and lathyrism are likely to become more prevalent in the setting of climate change leading to drought and flooding. Although modern advances in radiation therapy techniques have reduced the incidence of radiation myelopathy, patients with cancer are living longer due to improved treatments and may require reirradiation that can increase the risk of this condition. Immune checkpoint inhibitors are increasingly used for the treatment of cancer and are associated with a wide variety of immune-mediated neurologic syndromes including myelitis.

ESSENTIAL POINTS

Metabolic and toxic causes should be considered in the diagnosis of myelopathy in patients with particular clinical syndromes, risk factors, and neuroimaging findings. Some of these conditions may be reversible if identified and treated early, requiring careful history, examination, and laboratory and radiologic evaluation for prompt diagnosis.

Subacute Combined Degeneration of the Spinal Cord Induced by Nitrous Oxide Abuse: A Rare Patient Presentation to a Spine Surgery Clinic: Illustrative Case

Subacute combined degeneration (SCD) of the spinal cord is a disease involving the lateral and posterior columns of the spinal cord that can manifest in patients with vitamin B12 deficiency. Nitrous oxide (N2O)-induced SCD of the spinal cord is a result of N2O interfering with the metabolism of vitamin B12 and results in nervous system demyelination. This is an infrequent complication of N2O anesthesia; however, cases are rising with recreational N2O use. This case report describes a patient with SCD of the spinal cord induced by recreational N2O abuse. The patient presented to a spine surgery clinic with a 3-week history of progressive global weakness and paresthesias. After a detailed history and physical examination, the diagnosis was made and supported by various tests and imaging findings. Despite marked neurologic deficits, the patient's symptoms improved markedly with therapy and vitamin B12 supplementation. Spine surgery clinicians may be confronted with these cases and should be aware of this atypical presentation of SCD. As in our case, patients may present with neurologic deficits of unclear etiology. Neurologic dysfunction may be irreversible; therefore, accurate diagnosis, medical treatment, and complete neurologic evaluation are of the utmost importance to prevent additional progression.

The efficacy and tolerability of inhaled nitrous oxide in major depressive disorder: a systematic review and meta-analysis

BACKGROUND

Nitrous oxide (N2O) has been initially confirmed by clinical trials to benefit to patients with major depressive disorder (MDD). However, there needs to be a meta-analysis to compare the efficacy and tolerability of N2O in MDD.

METHODS

PubMed, EMBASE, and Cochrane Library were searched for relevant studies up to Jan 1st, 2023. The meta-analysis mainly compared the outcome of the change in depression severity scores, response, remission, and adverse events in patients with MDD receiving 50% N2O and placebo.

RESULTS

Four studies with 133 patients were eventually identified. We found that the N2O group and control group showed an overall significant difference in the change in depression severity score for patients at 2 h, 24 h, and 2 weeks or more (2 h, SMD =  - 0.64, 95% CI - 0.01 to - 0.28, p < 0.0001) (24 h, SMD =  - 0.65, 95% CI - 1.01 to - 0.29, p < 0.0001) (2 weeks, SMD =  - 0.76, 95% CI - 1.16 to - 0.36, p < 0.0001). For the response and remission rate, the long-term effect of N2O was also statistically significant (for the response, RR = 2.33, 95% CI 1.23 to 4.44, p = 0.01) (for the remission, RR = 4.68, 95% CI 1.49 to 14.68, p = 0.008). For safety outcomes, patients treated with N2O had higher odds of nausea or vomiting (RR = 10.15, 95% CI 1.96 to 52.59, p = 0.009).

CONCLUSION

Our study suggested that N2O has a rapid and long-lasting antidepressant effect in patients with MDD. However, the efficacy of lower or titrated concentration of N2O should be further investigated.

Nitrous oxide-induced myeloneuropathy: a case series

BACKGROUND

Nitrous oxide (N2O) is the second most common recreational drug used by 16- to 24-year-olds in the UK. Neurological symptoms can occur in some people that use N2O recreationally, but most information comes from small case series.

METHODS

We describe 119 patients with N2O-myeloneuropathy seen at NHS teaching hospitals in three of the UK's largest cities: London, Birmingham and Manchester. This work summarises the clinical and investigative findings in the largest case series to date.

RESULTS

Paraesthesia was the presenting complaint in 85% of cases, with the lower limbs more commonly affected than the upper limbs. Gait ataxia was common, and bladder and bowel disturbance were frequent additional symptoms. The mid-cervical region of the spinal cord (C3-C5) was most often affected on MRI T2-weighted imaging. The number of N2O canisters consumed per week correlated with methylmalonic acid levels in the blood as a measure of functional B12 deficiency (rho (ρ)=0.44, p=0.04).

CONCLUSIONS

Preventable neurological harm from N2O abuse is increasingly seen worldwide. Ease of access to canisters and larger cylinders of N2O has led to an apparent rise in cases of N2O-myeloneuropathy in several areas of the UK. Our results highlight the range of clinical manifestations in a large group of patients to improve awareness of risk, aid early recognition, and promote timely treatment.

Subacute Combined Degeneration of the Spinal Cord Secondary to Nitrous Oxide Abuse

Here, we report a case of subacute combined degeneration (SCD) of the spinal cord in the setting of nitrous oxide poisoning seen at the Medical Ward, Queen Elizabeth Hospital Birmingham Our patient was a 28-year-old lady who presented with impaired sensations in the lower limbs and difficulty walking for approximately one and a half months. Her clinical symptoms did not match common neurological conditions. Upon detailed history, she revealed that she had been frequently using nitrous oxide recreationally for several years. Although her baseline investigations were normal, her magnetic resonance imaging (MRI) of the spine showed bilateral symmetrical T2 hyperintense signal changes in the dorsal columns extending from C2 to C6 spinal segment. Based on history, clinical findings, and MRI of the cervical spine, the diagnosis of SCD of the spinal cord was made, and her symptoms fully resolved with treatment.

Nitrous oxide-induced subacute combined degeneration of the cord: diagnosis and treatment

Recreational use of nitrous oxide (N₂O) has increased rapidly in recent years and is now the second most commonly used recreational drug among young people in the UK. There has been a corresponding rise in cases of nitrous oxide-induced subacute combined degeneration of the cord (N₂O-SACD), a pattern of myeloneuropathy usually associated with severe vitamin B₁₂ deficiency. This can cause serious and permanent disability in young people but, if recognised early, may be effectively treated. All neurologists should be aware of N₂O-SACD and its treatment; however, there are currently no agreed guidelines. Based on our experience in East London, an area of high N₂O use, we provide practical advice on its recognition, investigation and treatment.

Nitrous oxide-induced neurotoxicity: Clinical characteristics and impacts on overall neurological impairments

Objective

The reports of the recreational use of nitrous oxide (N₂O) and its related neuropathy are increasing. However, it is unclear whether specific clinical characteristics are associated with the overall neurological impairments among these individuals.

Methods

We retrospectively included 20 hospitalized patients with N₂O-related neurological complaints between January 2016 and March 2021 at the West China Hospital of Sichuan University. Detailed demographic, clinical features, lab tests, and imaging data were collected. A functional disability rating score (FDRS) was calculated to determine the degree of neurological impairment. The relationships between the aforementioned factors and the FDRS sum score were explored.

Results

These individuals were aged between 16 and 30 years (mean ± SD: 21.90 ± 4.06). At admission, unsteady gait (95%, nineteen of twenty), weakness (95%, nineteen of twenty), and limb paresthesia (70%, fourteen of twenty) were the most common symptoms; decreased deep tendon reflexes (100%, nineteen of nineteen), reduced muscle strength (95%, nineteen of twenty), and impaired coordination (95%, nineteen of twenty) were frequently found. The FDRS sum scores ranged from 3 to 12. Among all the factors, admission from the emergency room (p = 0.033), decreased hemoglobin (p = 0.004) (without previous VitB12 supplements), decreased red blood cell (RBC) count (p = 0.004) (without previous VitB12 supplements), and increased mean corpuscular volume (p = 0.036) (with previous VitB12 supplements) positively correlated with the FDRS sum score.

Conclusion

Nitrous oxide (N₂O) could lead to severe neurological impairments among users. Abnormal RBC indicators at admission may be associated with a worse clinical presentation and need further attention. Population education about the consequences of N₂O consumption and control measures concerning access to N₂O should be further emphasized.

Mechanisms Involved in the Neurotoxicity and Abuse Liability of Nitrous Oxide: A Narrative Review

The recreational use of nitrous oxide (N₂O) has increased over the years. At the same time, more N₂O intoxications are presented to hospitals. The incidental use of N₂O is relatively harmless, but heavy, frequent and chronic use comes with considerable health risks. Most importantly, N₂O can inactivate the co-factor cobalamin, which, in turn, leads to paresthesia's, partial paralysis and generalized demyelinating polyneuropathy. In some patients, these disorders are irreversible. Several metabolic cascades have been identified by which N₂O can cause harmful effects. Because these effects mostly occur after prolonged use, it raises the question of whether N₂O has addictive properties, explaining its prolonged and frequent use at high dose. Several lines of evidence for N₂O's dependence liability can be found in the literature, but the underlying mechanism of action remains controversial. N₂O interacts with the opioid system, but N₂O also acts as an N-methyl-D-aspartate (NMDA) receptor antagonist, by which it can cause dopamine disinhibition. In this narrative review, we provide a detailed description of animal and human evidence for N₂O-induced abuse/dependence and for N₂O-induced neurotoxicity.

Strukturelle Gehirnveränderungen und Läsionen durch den Konsum illegaler Drogen und Psychedelika

Drogen können sowohl die Funktion wie auch die Struktur des Gehirns verändern. Gelegentlicher oder regelmäßiger Drogenkonsum ist in der Bevölkerung weit verbreitet. Daher ist die Kenntnis möglicher Nebenwirkungen und charakteristischer Bildbefunde bei Untersuchungen des Gehirns für den klinischen Alltag wichtig. Dieser Artikel beschreibt die für die am weitesten verbreiteten Substanzen typischen Komplikationen und morphologisch-radiologischen Veränderungen. Zu den möglichen Pathomechnismen gehören neurotoxische Effekte, die zu Leukenzephalopathie oder Hirnatrophie führen können, und vaskuläre Komplikationen wie Vasokonstriktion, Vaskulitis oder Hypertonus, durch die es zu intrazerebralen Blutungen oder Infarkten kommen kann. Da die klinische Präsentation oft unspezifisch ist, und die betroffenen Patienten ihren Drogenkonsum häufig verschweigen, ist das Erkennen typischer Bildbefunde essentiell für eine zuverlässige Diagnosestellung und zielgerichtete Therapie.

Peripheral polyneuropathy and acute psychosis from chronic nitrous oxide poisoning: A case report with literature review

RATIONALE

Nitrous oxide (NO) is a commonly used drug in medical practice, restoration, and the automobile industry. Recreational abuse is an emerging public health problem owing to its accessibility and drug properties.

PATIENT CONCERNS

A 25-year-old male was hospitalized with acute psychosis and lower-extremity sensorimotor proprioceptive ataxia due to nitrous oxide abuse.

DIAGNOSIS

Laboratory studies confirmed a vitamin B12 deficiency. Magnetic resonance imaging of the spinal cord showed normal findings. Electrophysiological testing confirmed length-dependent sensorimotor polyneuropathy, with a predominant motor component and axonal degeneration.

INTERVENTION AND OUTCOMES

Abstinence from toxic substances was suggested, and vitamin B12 substitution was introduced. The patient was lost to follow up.

LESSONS

Nitrous oxide toxicity is multisystemic and is thought to result from vitamin B12 inactivation. Recent case reports postulated direct paranodal lesions resulting from nitrous oxide consumption. Neurological, neuropsychiatric, and hematological toxicities are among those explored in this case report. Correction of the functional vitamin B12 status and nitrous oxide abstinence are essential in the treatment process.

Surgical Approach in Intraocular Tumors

Surgery in intraocular tumors is done for excision/biopsy and the management of complications secondary to the treatment of these tumors. Excision/biopsy of intraocular tumors can be done via fine-needle aspiration biopsy (FNAB), transretinal biopsy (TRB), partial lamellar sclerouvectomy (PLSU), and endoresection. FNAB, TRB, and PLSU can be used in tumors that cannot be diagnosed by clinical examination and other ancillary testing methods. PLSU is employed in tumors involving the iridociliary region and choroid anterior to the equator. Excisional PLSU is performed for iridociliary and ciliary body tumors with less than 3 clock hours of iris and ciliary body involvement and choroidal tumors with a base diameter less than 15 mm. However, for biopsy, PLSU can be employed with any size tumor. Endoresection is a procedure whereby the intraocular tumor is excised using vitrectomy techniques. The rationale for performing endoresection is based on the fact that irradiated uveal melanomas may cause complications such as exudation, neovascular glaucoma, and intraocular pigment and tumor dissemination (toxic tumor syndrome), and removing the dead tumor tissue may contribute to better visual outcome. Endoresection is recommended 1-2 weeks after external radiotherapy. Pars plana vitrectomy is also used in the management of complications including vitreous hemorrhage, retinal detachment, and epiretinal membrane that can occur after treatment of posterior segment tumors using radiotherapy and transpupillary thermotherapy. It is important to make sure the intraocular tumor has been eradicated before embarking on such treatment.

Analysis of clinical characteristics and prognostic factors in 110 patients with nitrous oxide abuse

PURPOSE

To review the clinical symptoms, auxiliary examination findings, and outcomes of patients with nitrous oxide (N₂ O) abuse, and analyze the factors that affect outcomes.

METHODS

Patients with N₂ O abuse treated in the Department of Neurology between January 2018 and December 2020 were included. The clinical data of these patients were collected, and follow-up was conducted to determine the outcomes.

RESULTS

The average age of the 110 patients with N₂ O abuse was 21.4 ± 4.2 years (range: 14-33 years). Clinical presentation primarily included neurological symptoms, such as limb numbness and/or weakness (97%), psychiatric symptoms, changes in appetite, and skin hyperpigmentation. Laboratory test results were characterized by vitamin B₁₂ deficiency (60%, 34 out of 57 cases) and high homocysteine level (69%, 31 out of 45 cases). Electromyography indicated mixed axonal and demyelination injury (92%, 80 out of 87 cases). Motor and sensory nerves were simultaneously involved, and injury primarily involved the lower limbs. One hundred and seven (97%) patients were clinically diagnosed with peripheral neuropathy, of whom 26 (24%) exhibited spinal abnormalities on magnetic resonance imaging, supporting a diagnosis of subacute combined degeneration. Treatment included N₂ O withdrawal and vitamin B₁₂ supplementation. Reexamination of six patients indicated that treatment was effective. Follow-up was completed for 51 patients. Thirty-four patients (67%) recovered completely, 17 patients (33%) had residual limb numbness, and only one patient experienced relapse. Sex was an independent prognostic factor; the outcomes of female patients were better than that of male patients.

CONCLUSION

The recreational use of N₂ O has largely expanded among youth in recent decades, which has become a growing public health concern in China. It highlights the importance of the recognition of various clinical symptoms, particularly limb numbness and/or weakness related to the cases of N₂ O abuse. The therapeutic administration of vitamin B₁₂ supplementation and N₂ O withdrawal can make the overall prognosis good, especially for female patients.

Nitrous Oxide: an emerging novel treatment for treatment-resistant depression

Stemming from the results of the historic STAR-D trial, it is evident that a significant subset of individuals (20-25%) with major depressive disorder (MDD) do not respond to conventional antidepressant medications. As a result, an emphasis has been placed on the development of novel therapeutics for MDD over the last two decades. Recently, substantial research efforts have been focused on the use of ketamine as an antidepressant whose mechanism of action is via the N-methyl-d-aspartate (NMDA) receptor. Another potential therapeutic compound of interest is nitrous oxide, which has been utilized for more than a century in multiple fields of medicine for its analgesic and anesthetic properties. Recent clinical studies suggest that nitrous oxide may be effective for treatment-resistant depression. In this review, we will discuss the administration of nitrous oxide as a psychiatric intervention, current use in psychiatry, putative mechanisms of action, and future directions highlighting knowledge gaps and other potential utilities in the field of psychiatry.

[Acute and chronic toxicities associated with the use and misuse of nitrous oxide: An update]

Nitrous oxide (N₂O) is used since the eighteenth century as an anesthetic and analgesic but also for recreational use. If the labelled uses of N₂O and their modalities are nowadays perfectly framed, the misuse of N₂O takes very alarming proportions among teenagers and young adults. This misuse is the cause of acute (hypoxia, barotrauma, burns, neuropsychiatric disorders) and chronic complications if repeated (myeloneuropathy, anemia, thrombosis, inhalant use disorder). The main mechanism of the latter is mainly related to a functional deficit in vitamin B12 induced by N₂O. The management of acute complications is symptomatic. The management of chronic complications is based on vitamin B12 supplementation. The best biomarker of chronic N₂O exposure is the elevation of the plasmatic level of methylmalonic acid. In all cases of recreational misuses, addiction treatment is necessary to prevent complications or their worsening by providing information in order to stop consumption.

Serum copper decrease and cerebellar atrophy in patients with nitrous oxide-induced subacute combined degeneration: two cases report

Background

Subacute combined degeneration (SCD) is a neurological complication commonly associated with vitamin B₁₂ deficiency. It can result from nitrous oxide (N₂O) abuse and cause neuropsychiatric symptoms. However, there has been no literature regarding alterations of serum copper and cerebellum in SCD patients.

Case presentation

We reported two cases of young SCD patients with histories of N₂O abuse. In these cases, elevated homocysteine, macrocytic anemia, spinal cord abnormalities, and peripheral nerve injuries were detected. In addition, decreased serum copper level and cerebellar atrophy were reported for the first time. The patients’ symptoms improved after withdrawal of N₂O exposure and vitamin B₁₂ supplements.

Conclusion

We reported two SCD cases with serum copper alteration and cerebellar atrophy after N₂O abuse for the first time. These might be crucial complements to the diagnosis of SCD.

Nitrous oxide-related neurological disorders: Clinical, laboratory, neuroimaging, and electrophysiological findings

BACKGROUND

Recreational N₂ O abuse is an important etiology of neurological impairment in young patients, which may easily be ignored clinically. Few current studies have investigated the characteristics or the effects experienced by its users. We aimed to explore any correlation between the clinical severity and biomarkers and spinal magnetic resonance imaging (MRI) abnormalities, identify independent factors associated with spinal MRI abnormalities, and ascertain factors affecting depression/anxiety in patients with N₂ O-related neurological disorders.

METHODS

Patients with N₂ O-related neurological disorders were enrolled retrospectively between February 2017 and July 2020. Their demographic, clinical, laboratory, neuroimaging, electrophysiological, and neuropsychological findings were analyzed. Correlation analyses were conducted using Spearman's or Pearson's correlation and linear regression analysis. Independent factors associated with spinal MRI abnormalities were identified using univariate and multivariate analyses.

RESULTS

The principal clinical manifestations of N₂ O-related neurological disorders (n = 63; 38 men, 25 women; mean age ± SD: 22.60 ± 4.46 years) were sensory disturbance, followed by gait disturbance and pyramidal tract damage. A significant negative correlation existed between serum vitamin B₁₂ levels and clinical severity (r = -0.309, p = .014), which disappeared after linear regression. An interval of less than 6 months between initial N₂ O abuse and hospitalization was independently associated with spinal MRI abnormalities (39.47% vs. 72.00%, respectively; χ²  = 6.40, p = .01). Thirty-eight (60.32%) and 40 (63.49%) patients experienced anxiety and depression, respectively. Moreover, the higher the clinical scores/serum homocysteine levels, the greater the severity of anxiety/depression (r = 0.442, p < .01; r = 0.346, p < .01; r = 0.477, p < .01; r = 0.324, p < .01).

CONCLUSIONS

The significant inverse correlation between initial vitamin B₁₂ levels and clinical severity could aid prognosis prediction in patients with N₂ O-related neurological disorders. Spinal MRI abnormalities were not related to clinical severity but depended on the time interval between initial N₂ O abuse and hospitalization. Anxiety and depression were common comorbidity in these patients, and their severity increased with the intensity of clinical impairment and/or serum homocysteine levels.

Electrophysiological characteristics of patients with nitrous oxide abuse

Objective: In the young generations with nitrous oxide abuse (N₂O), featured electrophysiological response of the peripheral neuropathy caused by nitrous oxide remains to be defined.Methods: Patients with nitrous oxide abuse (20 cases), two variants of Guillain-Barré syndrome (GBS), that is, acute inflammatory demyelinating polyradiculoneuropathy (GBS-AIDP, 19 cases) and acute motor axonal neuropathy (GBS-AMAN, 18 cases), as well as diabetic peripheral neuropathy (DPN, 20 cases) were enrolled into this study. Electrophysiological parameters including distal motor latency (DML), motor nerve conduction velocity (MNCV), sensory nerve conduction velocity (SNCV), amplitudes of compound muscle action potential (CMAP), and sensory nerve action potential (SNAP) were measured and analyzed by comparing the parameters between the aforementioned patients groups as well as normal control group (20 subjects).Results: Compared to normal control subjects, patients with nitrous oxide abuse showed prolonged DML, slower MNCV and SNCV in the limbs, lower amplitudes of CMAP in the median, tibial and peroneal nerves, and lower SNAP in median and ulnar nerves. Abnormalities of MNCV and amplitudes of CMAP in the lower limbs were significantly higher than that in the upper limbs . Abnormal electrophysiological features of patients with nitrous oxide abuse were dramatically different from those in GBS-AIDP or DPN patients, but similar to those in GBS-AMAN patients.Conclusions: Nitrous oxide abuse could cause abnormal electrophysiological response in the limbs. Some of the parameters (DML, MNCV, SNCV, CMAP and SNAP) appeared significantly different between the patients with nitrous oxide abuse, GBS with AIDP or AMAN, and DPN patients.Significance: Electrophysiological examination could be considered as an important supporting factor in differential diagnosis for nitrous oxide abuse, GBS with AIDP or AMAN, and DPN.

Metabolic and Toxic Myelopathies

Metabolic and toxic causes of myelopathy form a heterogeneous group of disorders. In this review, we discuss the causes of metabolic and toxic myelopathies with respect to clinical presentation, pathophysiology, diagnostic testing, treatment, and prognosis. This review is organized by temporal course (hyperacute, acute, subacute, and chronic) and etiology (e.g., nutritional deficiency, toxic exposure). Broadly, the myelopathies associated with dietary toxins (neurolathyrism, konzo) and decompression sickness present suddenly (hyperacute). The myelopathies associated with heroin use and electrical injury present over hours to days (acutely). Most nutritional deficiencies (cobalamin, folate, copper) and toxic substances (nitrous oxide, zinc, organophosphates, clioquinol) cause a myelopathy of subacute onset. Vitamin E deficiency and hepatic myelopathy cause a chronic myelopathy. Radiation- and intrathecal chemotherapy-induced myelopathy can cause a transient and/or a progressive syndrome. For many metabolic and toxic causes of myelopathy, clinical deficits may stabilize or improve with rapid identification and treatment. Familiarity with these disorders is therefore essential.

B12 Deficiency and Clinical Presentation in the Setting of Nitric Oxide Use

B12 deficiency can arise symptomatically from an array of varying pathologies including frank deficiency from strict vegan diets. Other high-risk contributing pathological conditions include chronic alcoholism, autoimmune disease, and chronic gastrointestinal inflammatory disorders, and it is also seen in those with a history of gastric surgery. Additionally, the elderly are at an increased risk as are patients prescribed certain medications. Uncommonly suspected causes of B12 deficiency include the abuse of recreational nitrous oxide (NO) given its interference with cobalt oxidation. Here, we report two cases of hypovitaminosis B12 in association with NO abuse in an effort to highlight an increasingly dangerous trend with recreational use. Importantly, we aim to increase visibility of this malady given that improperly diagnosed neurologic deterioration following NO anesthesia has been shown to become irreversible and may even result in death.

Clinical and MRI Differences Between Patients With Subacute Combined Degeneration of the Spinal Cord Related vs. Unrelated to Recreational Nitrous Oxide Use: A Retrospective Study

Objective: To explore the clinical and imaging characteristics of subacute combined degeneration of the spinal cord (SCD) related to recreational nitrous oxide (N₂O) use.

Methods: Clinical and imaging data were retrospectively collected from patients with SCD related to recreational N₂O use who were diagnosed and treated at Shengjing Hospital of China Medical University from January 2016 to June 2020. The clinical and imaging features of patients with recreational N₂O-related SCD were compared with those of patients with N₂O-unrelated SCD, who were diagnosed and treated during the same period of time.

Results: The study enrolled 50 patients (male/female: 22/28, age: 21.4 ± 4.7 years) with N₂O-related SCD and 48 patients (male/female: 27/21, age: 62.0 ± 11.4 years) with SCD unrelated to N₂O use. The most common signs/symptoms of the patients in both groups were limb numbness and weakness and unsteady gait, but the incidence of limb weakness, unsteady gait, disorders of urination and defecation, anorexia, reduced deep sensation in lower limbs, ataxia, and positive Babinski sign were lower in the N₂O-related SCD group than those in the N₂O-unrelated SCD group (P < 0.05). The functional disability rating score of patients in the N₂O-related SCD group (median: 3, IQR: 2–5) was also significantly lower than the score in the N₂O-unrelated SCD group (median: 5, IQR: 4–7) (P < 0.05). The serum vitamin B12 level was significantly lower in the N₂O-unrelated SCD group (median: 96 pg/mL, IQR: 50–170 pg/mL) than the level in the N₂O-related SCD group (median: 218 pg/mL, IQR:121–350 pg/mL) (P < 0.05), while both groups had similarly increased levels of homocysteine (P > 0.05). Compared with the N₂O-unrelated SCD patients, more patients with N₂O-related SCD had abnormal spinal magnetic resonance imaging (MRI) scans (80.0 vs. 64.2%). The patients with N₂O-related SCD also had wider spinal lesions on sagittal MRI (5.3 ± 0.8 mm vs. 4.2 ± 1.0 mm), fewer spinal segments with lesions (median: 5, IQR: 4–6 segments vs. median: 6, IQR: 5–7.5 segments), and a higher incidence of the inverted V sign on axial MRI (72.0 vs. 31.2%) (all P < 0.05).

Conclusion: The recreational use of N₂O has become an important cause of SCD in young patients. Compared with the N₂O-unrelated SCD patients, the N₂O-related SCD patients had less severe clinical presentations, less obvious decrease in serum VB12 levels, and more obvious MRI changes.

Metabolic and Toxic Myelopathies

PURPOSE OF REVIEW

This article describes the clinical presentation, relevant diagnostic investigations, and treatment of metabolic and toxic myelopathies.

RECENT FINDINGS

Metabolic myelopathies, including those due to deficiency of vitamin B12, folate, copper, or vitamin E, are preventable and typically respond to supplementation. In metabolic myelopathy, early recognition and treatment are important to reduce morbidity, particularly due to subacute combined degeneration of the spinal cord. Toxic myelopathies, including those due to medical interventions (eg, methotrexate, radiation), dietary toxins (eg, lathyrism, konzo), and drugs of abuse (eg, heroin), typically result in permanent neurologic deficits. Toxic myelopathy due to hepatic dysfunction may be reversible if patients receive early intervention, whereas nitrous oxide myelopathy responds to vitamin B12 replacement and cessation of exposure. In toxic myelopathy, it is best to avoid the provoking factor when possible or attempt to mitigate risk by identifying risk factors for developing myelopathy.

SUMMARY

Metabolic and toxic myelopathies are important causes of morbidity that require a high index of suspicion for diagnosis.

Subacute combined degeneration of the spinal cord in functional vitamin B12 Deficiency states

Vitamin B12 is an essential enzymatic cofactor in multiple cellular metabolic pathways. Deficiency states can arise as a result of both depletion of absolute systemic levels and pathological processes that block its ability to act as an enzymatic cofactor. The latter is also known as functional vitamin B12 deficiency. This can cause a variety of systemic, haematological, and neurological manifestations, some of which may be irreversible if not promptly treated. Neurological syndromes include subacute combined degeneration of the cord (SCDC), peripheral, optic, and autonomic neuropathies, and neuropsychiatric or cognitive deficits. This review presents a case series of vitamin B12 deficiencies leading to SCDC, and we include the clinical features, significant investigations, treatments, and prognoses.

Subacute combined degeneration of the cervical and dorsal spinal cord in a 40-year-old male patient: A case report

Subacute combined degeneration of the spinal cord is a neurologic complication of vitamin B12 deficiency. It presents as a potentially reversible demyelination of the posterior and lateral columns of the cervical and dorsal spinal cord. We present the case of a 40-year-old male with progressive sensory and motor deficit from the lower extremities ascending to the mid-thoracic region. A combination of laboratory tests and magnetic resonance imaging confirmed the diagnosis of subacute degeneration of the spinal cord due to vitamin B12 deficiency.

Isolated cortical vein thrombosis after nitrous oxide use in a young woman: a case report

Background

Nitrous oxide has become a popular inhalant as abused substance by young Chinese people in recent years. It has been mainly associated with medical conditions including megaloblastic anemia and myeloneuropathy.

Case presentation

We report a case of a 25-year-old high school graduate who had been abusing nitrous oxide for twenty months. She had a history of peripheral neuropathy and subacute combined degeneration in between. The young woman presented with headache, motor aphasia and right arm paralysis of eight hours after intermittently consuming nitrous oxide for one week. D-dimer was increased (1.1 mg/ml). Blood vitamin B12, folate, homocysteine and beta-HCG levels were normal. Head CT showed hemorrhagic infarction and subarachnoid hemorrhage. MR angiography and venography were normal. Head MRI identified left frontal isolated cortical vein thrombosis. Her muscle strength and verbal fluency significantly improved after initiation of Low Molecular Weight Heparin and serial head MRI showed continuous reduction in the size of thrombus.

Conclusions

For the first time nitrous oxide use is found to be related to isolated cortical vein thrombosis. Public education regarding the potential consequences of abusing nitrous oxide especially in high-risk individuals is urgently needed.

Subacute Combined Degeneration Secondary to Nitrous Oxide Abuse: Quantification of Use With Patient Follow-up

Subacute combined degeneration (SCD) is caused by demyelination of spinal cord white matter secondary to vitamin B12 (cobalamin) deficiency leading to core symptoms of spastic paresis and vibratory and proprioceptive deficits. Most common causes of B12 deficiency revolve around malabsorption and pernicious anemia; however, nitrous oxide (N2O) can also indirectly cause B12 deficiency by inactivating its biologically active form. We report a case of a patient who took advantage of the unregulated N2O market and presented with signs and symptoms of SCD secondary to N2O abuse. Prior to symptom onset, the patient reported approximately 3,000g of N2O inhalation within five days prior to symptom onset in addition to daily use three weeks prior. Work up revealed laboratory and imaging abnormalities consistent with SCD, although B12 levels were normal intrinsic-factor-blocking (IFB) antibodies were present. Appropriate treatment was undertaken, and the patient was followed up at one week and one month with noticeable clinical improvements. Similarities of this patient to literature include the classic presenting symptoms of SCD and the gradual symptomatic improvement with B12 injections and N2O abstinence. This case is remarkable due to SCD occurrence after recreational N2O abuse, objective quantification of N2O intake over a specified time period to induce SCD, occurrence secondary to N2O inhalation, positive IFB antibodies, and symptomatic presentation with B12 values within normal limits. This report highlights the dangers associated with N2O abuse and moving forward awareness of this case can be referenced to aid in educating members of our communities at risk for substance abuse.

The clinical and subclinical features of spinal cord injury on magnetic resonance imaging of patients with N2O intoxication

Nitrous oxide (N₂O) is a weak anesthetic gas that was first used in 1844 in the field of dental anesthesia. However, currently, N₂O is being abused for entertainment purposes in the form of N₂O-filled balloons, called funky balls, which can cause many adverse effects, especially nervous system injury. This study aimed to investigate the detailed clinical and subclinical features associated with N₂O intoxication. We retrospectively reviewed 47 patients diagnosed with N₂O intoxication, from May 2018 to July 2019, and collected demographic data, clinical and laboratory tests, and spinal cord magnetic resonance imaging (MRI) findings. The mean time of funky ball use was 8.8 months, with a mean use of 36.3 balls per day. All patients presented with superficial sensory disorders. Reductions in muscle strength, decreased vibration sensation, and decreased or lost tendon reflexes were the most common clinical signs of N₂O intoxication. Romberg sign and Lhermitte sign were observed in 39 patients (83%) and 21 patients (44.7%), respectively. Spinal cord lesions on MRI were observed in 32 patients (68.1%), which mostly presented with an inverted V sign. The total duration of N₂O use, the number of days of using N₂O per week, and the presence of Lhermitte sign (P<0.05) were significantly different between patients with and without spinal cord lesions on MRI. Serum levels of homocysteine and vitamin B12 were significantly different between the time of admission and discharge (P<0.05). Our study indicated that the days of using N₂O per week was significantly associated with Spinal Cord Injuries (SCI) on MRI. According to the Receiver Operating Characteristic (ROC) curve analysis, a cutoff days of using per week value of 2.5 days could predict SCI with a sensitivity of 81.3%, a specificity of 73.3%, and an area under the ROC curve (AUC) of 0.813. Changes in the serum levels of homocysteine and vitamin B12 were effective markers for the evaluation of treatment response.

Subacute combined degeneration induced by nitrous oxide inhalation: Two case reports

RATIONALE

Nitrous oxide (N2O), commonly known as "laughing gas," is being increasingly abused by young people as a recreational drug; this can subsequently result in myelopathy and peripheral neuropathy, however, in China, few cases of neurologic deterioration by N2O abuse have been reported.

PATIENT CONCERNS

Herein, we present 2 patients who developed progressive limb weakness, numbness, and ataxia. Both of them had recreationally inhaled N2O intermittently for a long time.

DIAGNOSIS

Subacute combined degeneration (SCD) based on myelopathy and polyneuropathy after N2O abuse.

INTERVENTIONS

The 2 patients were treated with cessation of N2O inhalation, methylcobalamin capsule 500 μg tid (ter in die, which means 3 times a day), and compound vitamin B 1 tablet tid p.o.(per os, which means taken orally) for 1 month.

OUTCOMES

The symptoms of altered sensation and the patients' gait improved significantly.

LESSONS

The 2 cases raise awareness of the important mechanisms of N2O neurotoxicity, and clinicians should be made fully aware of such substance-related diseases. The incidence of N2O -induced neurotoxicity is insufficiently recognized and should be considered as an important cause of SCD, especially in adolescents with undifferentiated weakness and abnormal sensation; this is essential because serious complications such as irreversible paralysis can result from the absence of early diagnosis and treatment.

Clinical-radiological dissociation in a patient with nitrous oxide-induced subacute combined degeneration: a case report

Background

Several recent studies have reported subacute combined degeneration (SCD) induced by nitrous oxide (N₂O) abuse. However, the association between the evolution of dynamic neuroimaging and clinical manifestations has not been reported in patients with N₂O-induced SCD.

Case presentation

We described the case of a 24-year-old man who developed SCD with inverted V-sign hyperintensities over the posterior aspect of the spinal cord caused by frequent, excessive N₂O inhalation. One month after treatment, his weakness and paresthesia resolved and serum vitamin B₁₂ levels exceeded the normal levels. However, the hyperintensities had extended horizontally and longitudinally on T2-weighted magnetic resonance imaging (MRI), compared to those on the initial scan. Two months after treatment, the patient experienced some residual numbness in the distal limbs, and his serum homocysteine levels were normal, but the abnormal signals seen on cervical T2-weighted MRI had decreased only slightly compared to those seen on the one-month follow-up MRI. The evolution of conventional MRI findings lagged compared to the clinical manifestation, which was suggestive of a clinical-radiological dissociation.

Conclusions

Clinical-radiological dissociation might have occurred in this case because T2-weighted imaging was not sensitive enough to reveal cytotoxic edema. Moreover, the serum vitamin B₁₂ level is not a good indicator of cellular vitamin B₁₂. Thus, clinicians should recognize this phenomenon, comprehensively assess the condition of patients with N₂O-induced SCD, and avoid terminating treatment based on the resolution of clinical symptoms and serological results.

Pernicious azotaemia? A case series of subacute combined degeneration of the cord secondary to nitrous oxide abuse

Nitrous oxide abuse is a rare cause of vitamin B12 deficiency and consequent subacute combined degeneration of the spinal cord. Worldwide and Australian statistics indicate that recreational use of nitrous oxide is increasing. We report four cases of females aged 18-24 years presenting with clinical symptoms of subacute combined degeneration of the spinal cord. MRI during admission demonstrated the classic findings of T2 hyperintensity, predominantly within the dorsal columns of the spinal cord, with variable involvement of the lateral corticospinal tracts. These cases highlight the ready availability of nitrous oxide and the fact that heavy prolonged recreational use is occurring in the community. It is important that clinicians in emergency and community settings are alerted to this unusual cause of subacute combined degeneration of the spinal cord because early aggressive vitamin B12 replacement together with behavioural change can reverse this disabling neurological syndrome.

Should nitrous oxide ever be used in oncology patients receiving methotrexate therapy?

Nitrous oxide (N₂ O) is frequently used for short anesthesia/analgesia in children undergoing painful or repetitive procedures. Children with acute lymphoblastic leukemia (ALL) require repeated lumbar punctures with direct instillation of intrathecal chemotherapy, usually the anti-folate agent methotrexate, during their treatment. These procedures are frequently performed under anesthesia. Concerns have been intermittently raised about a drug interaction between methotrexate and N₂ O that may potentiate the undesirable side effects of methotrexate, including neurotoxicity. However, the clinical evidence consists mainly of isolated case reports leading to a lack of consensus among pediatric anesthetists about the relative risk benefits of using N₂ O in children with ALL. In this article, we review the biochemical basis and scientific observations that suggest a significant interaction between N₂ O and methotrexate due to their dual inhibition of the key enzyme methionine synthase. The possible role of this interaction in potentiating neurotoxicity in children with cancer is discussed, and arguments and counterarguments about the clinical significance of this largely theoretical relationship are explored. Following comprehensive review of all the available data, we make the case for the circumstantial evidence being sufficiently compelling to prompt a review of practice by pediatric anesthetists and call for a precautionary approach by avoiding the use of N₂ O in children receiving concurrent methotrexate.

The sharp rise of neurological disorders associated with recreational nitrous oxide use in China: a single-center experience and a brief review of Chinese literature

INTRODUCTION

In recent years, there has been a sharp increase in the number of patients with neurological disorders associated with recreational use of nitrous oxide (N₂O) in China. Here, we summarize the clinical characteristics of patients with neurological disorders associated with N₂O abuse diagnosed in our Hospital. Further, we conducted a literature search on recent cases reported in mainland China to improve the awareness of the outbreak of neurological disorders associated with N₂O abuse.

METHODS

We retrospectively collected data of patients diagnosed with neurological disorders associated with recreational use of N₂O in Shengjing Hospital of China Medical University from January 2018 to June 2019, and performed a literature search using the "nitrous oxide" and "neurological disorder" as keywords in the Chinese literature databases of WANFANG and CNKI and the English literature databases of Pubmed and Web of Science RESULTS: We enrolled 43 patients (average age: 21.9 ± 3.3 years). The main clinical manifestations were weakness and paresthesia in the four extremities and unsteady gait. Further, most patients showed significantly lower levels of serum vitamin B12 (169.4 ± 79.1 pg/mL) and increased homocysteine levels (78.1 ± 32.2 μmol/L). MRI of the spinal cord showed longitudinal high T2 signal lesions in the dorsal spinal cord in some patients. Moreover, electromyography showed sensory and motor nerve axonal damage combined with demyelination, which was relatively more severe in the lower limbs. There was rapid improvement of the symptoms after treatment with intramuscular injections of vitamin B12 and the overall prognosis was good. The literature search indicated that the number of published papers and related patients showed a rapid annual increase since the first Chinese case reported in 2016 CONCLUSION: Recreational use of N₂O is an emerging public health problem in China that needs prompt action from the society and government. Early diagnosis and treatment allow a good overall prognosis.

The Role of Vitamin B12 in the Management and Optimization of Treatment in Patients With Degenerative Cervical Myelopathy

STUDY DESIGN

Narrative review.

OBJECTIVES

To discuss the relationship between degenerative cervical myelopathy (DCM) and vitamin B12 deficiency. Specifically, it is the aim to outline the rational for future research into assessment and therapeutic optimization of vitamin B12 in the treatment of DCM.

METHODS

Literature review.

RESULTS

DCM is the commonest cause of spinal cord impairment, with an average age of presentation in the sixth decade. Patients at this age have also been reported to have a high prevalence of vitamin B12 deficiency, with estimates of up to 20% in the elderly. Vitamin B12 deficiency can result in subacute combined degeneration of the spinal cord (SACD), and several case reports have pointed to patients with both DCM and SACD. Both SACD and reversible compressive injury due to DCM necessitate remyelination in the spinal cord, a process that requires adequate vitamin B12 levels. Basic science research on nerve crush injuries have shown that vitamin B12 levels are altered after nerve injury and that vitamin B12 along with dexamethasone or nonsteroidal anti-inflammatory drugs can reduce Wallerian degeneration. Furthermore, it has been suggested that a combination of B-vitamins can reduce glutamate-induced neurotoxicity.

CONCLUSIONS

Given the high prevalence of clinical and subclinical vitamin B12 deficiency in the elderly, the role of vitamin B12 in myelination, and vitamin B12 deficiency as a differential diagnosis of DCM, it is important to investigate what role vitamin B12 levels play in patients with DCM in terms of baseline neurological function and whether optimization of vitamin B12 levels can improve surgical outcome. Furthermore, the routine assessment of vitamin B12 levels in patients considered for DCM surgery should be considered.