Carbon disulfide induced polyneuropathy: sural nerve pathology, electrophysiology, and clinical correlation

Effect of environmental toxicants on neuronal functions

In the last few years, neurodegenerative diseases like Alzheimer's disease (AD) and Parkinson's disease (PD) have attracted attention due to their high prevalence worldwide. Environmental factors may be one of the biggest reasons for these diseases related to neuronal dysfunctions. Most of neuronal disorders are strongly associated with pre- and postnatal exposure to environmental toxins released from industries. Some of the neurotoxic metals such as lead, aluminum, mercury, manganese, cadmium, and arsenic as well as some pesticides and metal-based nanoparticles have been involved in AD and PD due to their ability to produce senile/amyloid plaques and NFTs which are the main feature of these neuronal dysfunctions. Exposure to solvents is also majorly responsible for neurodegenerative disorders. The present review highlights the impact of omnipresent heavy metals with some other neurotoxins on human health and how they give rise to neuronal dysfunctions which in turn causes socio-economic consequences due to increasing pollution worldwide. Graphical abstract.

Clinical description of toxic neuropathies

Toxic neuropathy, although rare, is an important consideration in the setting of a known or suspected toxic exposure in the workplace or other environment. This chapter discusses the clinical and electrodiagnostic evaluation of peripheral neuropathies, highlighting findings that direct further workup and may point to specific toxins as etiology. The difficulty of establishing causality of a toxin in relation to peripheral neuropathy is discussed; guidelines for establishing causality are presented. Examples of common industrial toxins are listed, including their typical industrial uses and their mechanisms of action in producing neuropathy. Characteristic clinical presentations of specific toxic neuropathies are highlighted with selected case studies.

Occupational neurotoxic diseases in taiwan

Occupational neurotoxic diseases have become increasingly common in Taiwan due to industrialization. Over the past 40 years, Taiwan has transformed from an agricultural society to an industrial society. The most common neurotoxic diseases also changed from organophosphate poisoning to heavy metal intoxication, and then to organic solvent and semiconductor agent poisoning. The nervous system is particularly vulnerable to toxic agents because of its high metabolic rate. Neurological manifestations may be transient or permanent, and may range from cognitive dysfunction, cerebellar ataxia, Parkinsonism, sensorimotor neuropathy and autonomic dysfunction to neuromuscular junction disorders. This study attempts to provide a review of the major outbreaks of occupational neurotoxins from 1968 to 2012. A total of 16 occupational neurotoxins, including organophosphates, toxic gases, heavy metals, organic solvents, and other toxic chemicals, were reviewed. Peer-reviewed articles related to the electrophysiology, neuroimaging, treatment and long-term follow up of these neurotoxic diseases were also obtained. The heavy metals involved consisted of lead, manganese, organic tin, mercury, arsenic, and thallium. The organic solvents included n-hexane, toluene, mixed solvents and carbon disulfide. Toxic gases such as carbon monoxide, and hydrogen sulfide were also included, along with toxic chemicals including polychlorinated biphenyls, tetramethylammonium hydroxide, organophosphates, and dimethylamine borane. In addition we attempted to correlate these events to the timeline of industrial development in Taiwan. By researching this topic, the hope is that it may help other developing countries to improve industrial hygiene and promote occupational safety and health care during the process of industrialization.

Subtle Changes in Cutaneous Nerves and Sural Nerve Biopsy in a Patient With Fabry's Disease

We report the clinical manifestations, and sural nerve and skin biopsy findings in a patient with Fabry's disease who had normal renal function. The patient had a typically painful neuropathy with an increase of sensory thresholds in quantitative sensory tests and a low level of serum alpha-galactosidase. Although the sural nerve biopsy revealed electron-dense bodies in the perineurial cells, normal axon and myelin structures and even the fiber density of large and small myelinated fibers were noted. However, the cutaneous nerve biopsy study showed early changes in the small-fiber neuropathy. The data indicate that a cutaneous nerve biopsy study can be an adjuvant diagnostic tool in some patients with Fabry's disease and a normal renal function.

Neurobehavioral and clinical effects in workers exposed to CS2

OBJECTIVES

Diffuse vascular encephalopathy, parkinsonism and peripheral polyneuropathy (PNP) due to CS(2) exposure are known since long. Data concerning low exposure are sparse. The current study aimed to evaluate whether the decrease of exposure below the threshold limit value (TLV) of 31 mg/m(3) results in an absence of neurological health effects using the same health outcomes as in the first study.

METHODS

The study was conducted in a group of workers of a viscose rayon plant and a control group (CG, n=66). The exposed group was divided into two groups, according to the average CS(2) exposure being below (EG1; n=60) or above 31 mg/m(3) (EG2; n=25). If the current TLV seemed insufficient to prevent effects, the analysis was repeated with three subgroups (10, >10 to 30, >30 mg/m(3)) to estimate the NOEL. Every participant filled in the neurotoxicity symptom checklist (NSC-60) and the Q16. Clinical neurological examination, computer-assisted neurobehavioral tests (NES) and neurophysiological examinations (nerve conduction velocities and electromyography (EMG)) were performed.

RESULTS

Sensorimotor complaints (NSC-60) were significantly worse in both EG1 and EG2 compared to CG (p=0.032) and both exposure groups had a higher proportion of positional tremor compared with CG (p=0.046). Finger tapping in the dominant and non-dominant hand (NES) was worse in EG1 and EG2 compared with CG (both p<0.001). A significant increase in sural nerve SCV, a significant decrease in sural nerve SNAP amplitude and duration and sympathetic skin response (SSR) amplitude, and higher prevalence of EMG abnormalities and PNP was also found in both EG1 and EG2 (p<0.003). All effects remained significant after controlling for possible confounding factors. Further analysis suggested that even average CS(2) exposures of 10 mg/m(3) could still cause effects on positional tremor, finger tapping dominant and non-dominant hand, sural nerve amplitude, SSR amplitude and EMG abnormalities.

CONCLUSIONS

An excess of psychomotor slowing, tremor and PNP was found in workers on average exposed to CS(2) concentrations below 31 mg/m(3). Data suggest that even average exposures as low as 10 mg/m(3) can cause the deleterious effects. This indicates that the current TLV insufficiently protects against neurological effects and, as a consequence, should be lowered.

Toxic neuropathies

Many substances, organic and manufactured, may induce peripheral nerve damage when exposed to them. The expected clinical phenotype is of a distal, sensory or sensorimotor polyneuropathy, often painful, with axonal characteristics on electrodiagnostic and histopathologic analysis. Treatment is limited; often, the only effective management is supportive care and avoidance from or removal of the offending toxin. Fortunately, the majority of toxic neuropathies are self-limited and improves gradually after toxin elimination.

Effect of occupational exposure to rayon manufacturing chemicals on skin barrier to evaporative water loss

To evaluate the effects of the occupational exposure to rayon manufacturing chemicals (RMC, containing predominantly carbon disulfide (CS(2)) and minor sulfuric acid) in a rayon factory on the basal transepidermal water loss (TEWL), barrier integrity (BI), and sequential increasing TEWL profiles. Six Thais and five Chinese workers in the spinning department of a rayon manufacturing plant and five healthy unexposed controls were recruited as the test subjects. An area of 4.5 x 5.5 cm on the mid-side of the volar forearm on the right hand was stripped by means of moderate pressure with commercially available adhesive tape by the same technician throughout the experiment. The skin was progressively stripped until glistening. TEWL was measured at every three and five tape strips on the right hand. The corresponding site on the left hand was measured parallel as the self-control. We found significant differences in basal TEWL and in BI between Chinese workers and Chinese controls, and between Thai workers and Chinese workers, respectively. Two-stage patterns of progressive TEWL profiles were found in such a chronic and repeated occupational exposure to RMC containing CS(2). The occupational exposure to RMC could result in the perturbation of the skin barrier function. Basal TEWL might be more sensitive to chronic skin irritant exposure. The TEWL profile achieved to the glistening stage might be necessary to avoid erroneous pattern estimation. Due to the lack of Thais control in this study, the racial difference in response to the RMC warrants further study.

The effect of personal factors on the relationship between carbon disulfide exposure and urinary 2-thiothiazolidine-4-carboxylic acid levels in rayon manufacturing workers

BACKGROUND

Few studies have been conducted to explore how personal factors-personal hygiene, personal protective equipment, and skin exposure affect the exposure-dose relationship in workers exposed to carbon disulfide (CS(2)).

METHODS

Personal environmental monitoring of airborne CS(2) and 2-thiothiazolidine-4-carboxylic acid (TTCA) levels in post-shift urine were determined for sixty-five rayon workers. The personal factors affecting the CS(2)-TTCA relationship were measured by questionnaire and dermatological diagnosis.

RESULTS

In simple linear regression analyses, we found shower right after work, respirator, gloves, apron, and skin disease were significantly associated with U-TTCA levels among all personal factors. Skin disease was, however, the only personal factor that remained significant throughout multivariate linear regression analyses.

CONCLUSIONS

In this study, the personal factor like host's skin disease was found to possibly affect the relations of U-TTCA to the occupational exposure to CS(2). The skin exposure to CS(2) for those who have skin problems on the sites possibly or potentially exposed to CS(2) in the occupational environment such as in the rayon manufacturing process is noteworthy. Workers with susceptible skins should either be assigned to work in areas without contacting hazardous materials directly or required to wear appropriately protective clothing.

Accumulation of urinary 2-thiothiazolidine-4-carboxylic acid (TTCA) among workers occupationally exposed to carbon disulfide for 1 week

OBJECTIVES

To investigate if carbon disulfide (CS(2)) accumulates after a 1-week exposure period, and how the work-shift duration and exposure magnitude affects this accumulation for the workers in viscose rayon industry.

METHODS

Six 8-h and seven 12-h workers in the spinning department historically known to be exposed to high air CS(2) were recruited as the exposed groups. Seven workers from other non-CS(2)-exposed departments were recruited as non-exposure controls. Exposure monitoring covered a full work shift with personal breathing zone monitoring. Urine was collected pre- and post-shift every day throughout the 5 consecutive days. 2-Thiothiazolidine-4-carboxylic acid levels in the urine (U-TTCA) were determined.

RESULTS

No detectable values were found for airborne (<0.6 ppm) and urinary (<35 ng/ml) monitoring for the control groups. The exposure levels for a 12-h shift (11.3+/-1.47) (AM+/-S.D.) were significantly greater than for an 8-h shift (6.3+/-0.64). The linear accumulation trend for daily U-TTCA across the workdays was only significant for the 12-h shift at pre-shift. Statistical significance was found in the regression of the ratios for pre-shift U-TTCA to airborne CS(2) levels on the preceding day to the day of the exposure at pre-shift for a 12-h shift (r=0.98, P=0.02).

CONCLUSIONS

The U-TTCA accumulation for occupational exposure to CS(2) was exposure-magnitude-dependent. The linear equations derived in this study indicated that the U-TTCA increment at pre-shift for each additional daily 12-h exposure, after an adjustment for the CS(2) exposure level, was 0.02 mg/g creatinine/ppm of CS(2). The long-term exposure response under such repeated and intermittent conditions should be noteworthy.

Clinical course in patients with chronic carbon disulfide polyneuropathy

The natural course of clinical manifestations and electrophysiological changes were studied in six patients with carbon disulfide (CS(2)) induced polyneuropathy. All of the six patients worked in the cutting-machine department of a viscose rayon plant. The environmental monitoring was also conducted in the initial stage and followed up 3 years later. In the 3-year follow-up period, the neurological symptoms and signs persisted. The highest concentration of CS(2) in the cutting machine where these patients worked was about 100-200 ppm. Three years later, the highest concentration was decreased to between 10 and 20 ppm in the cutting machine of the new production line after the engineering control had been improved. Nerve conduction velocity (NCV) studies revealed persistent abnormality in motor and sensory NCVs. Although, a tendency to improvement was noted, it did not reach a statistical significance except for conduction velocity of sural nerve in sensory NCV. Sural nerve biopsy from one patient, 2 years after diagnosis showed degeneration of both axon and myelin and a predominant loss of large myelinated fibers. A remyelination process was also noted. We concluded that CS(2) intoxication may induce a persistent damage to the peripheral nerves even after CS(2) exposure had ceased for 3 years.

Biological monitoring of carbon disulphide: kinetics of urinary 2-thiothiazolidine-4-carboxylic acid (TTCA) in exposed workers

The objectives of this study was to establish the kinetics of urinary 2-thiothiazolidine-4-carboxylic acid (U-TTCA) for workers exposed to carbon disulphide (CS2) and to investigate the effects of volume and creatinine adjustment methods for urine measurement. Ten workers in the spinning department of a rayon factory were individually monitored for airborne CS2 concentrations, with consecutive urine samples collected for 24-38 hours after termination of exposure. The U-TTCA, urine volume and creatinine level were measured for each sample. First-order and biphasic kinetics were determined using the curve-fit method, for the measurement series. For the first-order kinetics linearity fit, statistically significant correlation coefficients of 0.74-0.98 and 0.86-0.99 were derived for the volume- and creatinine-adjusted methods, respectively. For the biphasic kinetics approach, the overall correlation coefficients were 0.544-0.999 and 0.171-0.999 for the first and second phases of the creatinine-adjusted method, respectively. A post-shift U-TTCA of 3.0 mg/g Cr. equivalent, 40% below the current BEI setting at nearly PEL exposed level, was found. In conclusion, first-order kinetic response was confirmed for U-ITCA. Both volume- and creatinine-based urine adjustment are satisfactory for TTCA assessment as a biomarker of individual CS2 exposure although the correlation for creatinine-based measurement was modestly superior to the volume-based analogue. Based on the results of this study,we recommend a re-evaluation of the current biological exposure index of 5 mg/g creatinine at a CS2 exposure level of 10 ppm.

Chemicals and gases

This article covers the major chemicals and gases that are considered to be of the most clinical relevance to the primary care provider. The reader is referred to other comprehensive textbooks of toxicology and occupational medicine for a complete discussion of the numerous additional products found in the workplace that may result in occupational exposure.

Encephalomyeloradiculoneuropathy following exposure to an industrial solvent

A 19-year-old male developed complaints including weakness of the lower extremities and right hand, numbness, dysphagia and urinary difficulties following a 2 month exposure to an industrial solvent constituted mainly of 1-bromopropane, but also containing butylene oxide, 1,3 dioxolane, nitromethane, and other components. Nerve conduction studies revealed evidence of a primary, symmetric demyelinating polyneuropathy. Evidence of CNS involvement came from gadolinium enhanced MRI scans of the brain, showing patchy areas of increased T2 signal in the periventricular white matter, similar scans of the spinal cord revealing root enhancement at several lumbar levels, and SSEP studies. The patient's symptoms had started to resolve following the discontinuation of the exposure, before he was lost to follow-up. Similar findings have been reported following 1-bromopropane exposure in rats. I hypothesize that this patient's symptoms may have been due to 1-bromopropane-induced neurotoxicity.