Lead neuropathy

A systematic review of clinical and laboratory findings of lead poisoning: lessons from case reports

Lead is one of the most toxic heavy metals in the environment. The present review aimed to highlight hazardous pollution sources, management, and review symptoms of lead poisonings in various parts of the world. The present study summarized the information available from case reports and case series studies from 2009 to March 2020 on the lead pollution sources and clinical symptoms. All are along with detoxification methods in infants, children, and adults. Our literature compilation includes results from 126 studies on lead poisoning. We found that traditional medication, occupational exposure, and substance abuse are as common as previously reported sources of lead exposure for children and adults. Ayurvedic medications and gunshot wounds have been identified as the most common source of exposure in the United States. However, opium and occupational exposure to the batteries were primarily seen in Iran and India. Furthermore, neurological, gastrointestinal, and hematological disorders were the most frequently occurring symptoms in lead-poisoned patients. As for therapeutic strategies, our findings confirm the safety and efficacy of chelating agents, even for infants. Our results suggest that treatment with chelating agents combined with the prevention of environmental exposure may be an excellent strategy to reduce the rate of lead poisoning. Besides, more clinical studies and long-term follow-ups are necessary to address all questions about lead poisoning management.

Is Chronic Exposure to Raw Water a Possible Risk Factor for Amyotrophic Lateral Sclerosis? A Pilot Case-Control Study

Background: The etiopathogenesis of amyotrophic lateral sclerosis (ALS) is still largely unknown. Methods: We performed a case-control study (33 cases and 35 controls) in Umbria, Italy. We investigated associations between common lifestyle, clinical factors, as well as environmental exposures potentially implicated with ALS onset. Face-to-face interviews were carried out. All cases were recruited and diagnosed according to El Escorial criteria. Case-control comparisons were made for educational and residential status, occupational exposures, and clinical and lifestyle factors prior to cases’ dates of diagnosis. Results: Our results showed an increased risk of ALS for subjects chronically exposed to raw water use (odds ratio (OR) = 6.55, 95% confidence interval (CI): 2.24–19.12). Garden activities showed a tight association with ALS as well, very likely as a consequence of chronic raw water exposure. Indeed, we could exclude an impact for pesticides, as no significant differences were observed in pesticide exposure in the two groups interviewed. However, cases were more often exposed to fertilizers. After adjustment for age, sex, and heavy physical activities, exposure to raw water was still associated with increased ALS risk (OR = 4.74, 95% CI: 1.33–16.85). Discussion: These findings suggest an association between ALS and exposure to raw water, which should be further investigated for the presence of chemicals interfering with nervous system functionality.

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.

Lead poisoning: a disease for the next millennium

The decline in the prevalence of childhood lead poisoning is a public health success story. However, nearly a million preschool-aged children in the United States alone have elevated BPb levels. Toxicity correlates with BPb concentrations and progresses from biochemical and subclinical abnormalities at levels around 10 micrograms/dL to coma and death at levels over 100 micrograms/dL. Treatment consists of the elimination of exposure, interruption of the pathway into the child, modification of diet to ensure adequate essential metal intake (calcium, iron), and on occasion, chelation therapy. The identification of children with the most lead poisoning depends on screening for exposure (questionnaire) or evidence of increased absorption (BPb test). Follow-up is crucial to maximize the effectiveness of any intervention.

Effects of low level exposure to lead on neurophysiological functions among lead battery workers

OBJECTIVES

Assessment of neurophysiological functions in workers with low level exposure to lead and evaluation of the efficacy of bone lead measurements in the prediction of effects of lead.

METHODS

Exposure to lead of 60 workers from a lead battery battery factory was estimated from historical blood lead measurements and analysis of lead in the tibial and calcaneal bones with x ray fluorescence. Peripheral and central nervous system functions were assessed by measuring conduction velocities, sensory distal latencies, sensory amplitudes, and vibration thresholds as well as by quantitative measurement of the absolute and relative powers and mean frequencies of different electroencephalograph (EEG) channels.

RESULTS

Sensory amplitudes, and to a smaller degree sensory or motor conduction velocities, showed a negative correlation with long term exposure to lead, most clearly with integrated blood lead concentration and exposure time. Vibration thresholds measured in the arm were related to recent exposure to lead, those measured in the leg to long term exposure. The alpha and beta activities of the EEG were more abundant in subjects with higher long term exposure to lead. Calcaneal lead content reflected short term exposure, tibial lead content reflected long term exposure. Blood lead history showed a closer relation with effects of lead than the tibial or calcaneal lead concentrations.

CONCLUSIONS

Vibratory thresholds, quantitative EEG, and to a smaller extent the sensory amplitude, provide sensitive measures of effects of lead in occupationally exposed adults. Most accurate estimates of health risks induced by lead can be obtained from a good history of blood lead measurements. If such a history of blood lead concentrations is not available, analysis of bone lead may be used for the assessment of health risks.

Effects of exposure to lead on selected biochemical and haematological variables

Blood and urine samples were taken from 34 persons occupationally exposed to lead and from 56 non-exposed control persons and blood lead and haemoglobin concentrations, red blood cell count, erythrocyte glutathione peroxidase (GSH-peroxidase) and acetylcholinesterase (AChE), and urinary delta-aminolevulinic acid were determined. Blood lead concentrations of the lead-exposed subjects were within the range of generally accepted as safe for occupationally-exposed adults in many countries (i.e. below 50 micrograms Pb/dl blood). Yet, significant dose-dependent elevations were found in erythrocyte GSH-peroxidase and urinary delta-aminolevulinic acid. The urinary delta-aminolevulinic acid concentration of lead-exposed smokers was significantly elevated over that of lead-exposed non-smokers. Smoking did not effect the urinary delta-aminolevulinic acid concentration of control persons. In addition, a statistically significantly lower red blood cell count was observed in the lead-exposed group. Our results indicate that the above described safety standard for blood lead concentrations in occupationally exposed adults, although generally accepted, needs revision.

Visual evoked potentials N75 and P100 latencies correlate with urinary delta-aminolevulinic acid, suggesting gamma-aminobutyric acid involvement in their generation

Pattern reversal visual evoked potentials were recorded from 31 subjects who were occupationally exposed to lead and 54 non-exposed controls. No significant effects of lead were observed in the general subject population. However, when only non-smokers (17 lead-exposed and 27 controls) were evaluated, significant effects were found. The P100, but not the N75, latency was significantly prolonged in the lead-exposed group, and this correlated with both blood lead level and age. Nevertheless, both the N75 and P100 latencies correlated with the concentration of delta-aminolevulinic acid (delta-ALA) in urine and age. This, at least in part, could be due to elevated delta-ALA levels competing at gamma-aminobutyric acid (GABA) receptor neurons. This is consistent with the fact that GABA receptor neurons are involved along the entire length of the visual pathway. The results indicate that lead affects neural function even at permitted levels of exposure, and that this level should be reduced.

Neuropsychological effect of lead in occupationally exposed workers: a critical review

In their discussion of field testing of health effects of environmental and industrial toxins, Gullion and Eckerman make the following observations which can be applied to the current literature survey: "The general inattention to methodological consistency makes it difficult to integrate the research to date into a clear picture of what is known and not known about the effects of toxic substances on human behavior. In view of the variation in methods of subject selection, measurement, and statistical analysis, the completion of a series of studies of a particular toxic substance does not assure that there has been a concurrent accumulation of reliable knowledge about the effects of that substance. Apparent replications or failures to replicate a significant relationship must be evaluated carefully, since different studies may have measured different things in different populations." Therefore, the issue of psychological and neuropsychological effects of low-level lead exposure in adults remains to be resolved in the studies reviewed. The methodologies were so varied and the cultures in which the studies were conducted so diverse that it is impossible to generalize across findings. For example, studies were conducted in the U.S., Denmark, Sweden, Finland, and Australia. Although, in some instances, equivalent versions of neuropsychological and psychological tests were used, this was generally not the case. Nevertheless, a few general statements can be made. Studies that have been carried out in recent years are beginning to pay attention to more methodology and therefore do a much better job of controlling for possible confounding variables. Also, their statistical methods are more sophisticated and reporting techniques are superior to the earlier investigations in this area. The issue of whether current blood lead levels or cumulative levels are preferable is still unresolved with regard to the relationship of neuropsychological impairment. In the area of psychosocial functioning, there appears to be at least some evidence to support the observation that increased irritability and fatigue may lead to the interpersonal problems noted in various studies. However, this observation may be related to other factors which have not been controlled for, such as the workers' attitudes toward their job, level of motivation, and overall level of mental health. With regard to neuropsychological functions, there is some suggestive preliminary evidence for subtle changes in the ability to process information quickly.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of long-term lead intoxication on the nervous system of the chicken

In order to study the possible etiologic role of lead in human motor neuron disease we produced chronic lead intoxication in the chicken by daily administration of lead acetate. Control animals received sodium acetate. During life, periodic measurements were made of motor function, motor nerve conduction velocity and response amplitude. After sacrifice, histologic analysis was performed on spinal cord, peripheral nerve and muscle. A syndrome was produced characterized by a fall in motor response amplitude, spinal motor neuron degeneration, motor axonal loss and atrophy of muscle, similar to that seen in human motor neuron diseases.

Spinal origin of human lead neuropathy: this paper marks the 150th anniversary of Paralysie de Plomb ou Saturnine by L. Tanquerel des Planches

One hundred fifty years ago a young but distinguished French scientist, L. Tanquerel des Planches, published a most comprehensive work dealing with almost every known clinical, epidemiological, and occupational aspect of lead poisoning, Traité des Maladies de Plomb ou Saturnines exposing in its second volume, Paralysie de Plomb ou Saturnine his invaluable experience on lead palsy. Among his ideas, based on a rather unique accumulation of human cases of lead palsy, the theory of the neurotoxic action of lead on the spinal cord is of outstanding importance. This site and the mode of action of lead have long been unsettled, although both the nineteenth century classics in neurology and the classics in industrial medicine of the first half of the twentieth century have contributed to solving the pathophysiology of lead palsy. The contributions from these reports, which concur with Tanquerel's assumptions, are presented and discussed. It must be emphasized, however, that only with the advent of electrophysiology has it become possible definitely to recognize the spinal cord involvement as the cause of lead neuropathy. The hypothesis of the axonal degeneration of the "dying back" variant, starting in the biochemical lesion of perikaria of the anterior horn cells in the spinal cord, is in full agreement with both the electromyographic signs of denervation and the electroneurographic normal range of conduction velocity. This presumptive conclusion confirming the spinal origin of human lead neuropathy is very much in line with the concepts of Tanquerel des Planches.

An electroneurographic assessment of subclinical lead neurotoxicity

While heavy exposure to inorganic lead is capable of inducing symptomatic neuropathy in man, the subclinical neuropathy due to low levels of occupational lead exposure remains to be proved. The reported results of electroneurographic studies on lead workers, however, have been controversial. In this study, 40 lead smeltery workers and 50 non-exposed referents were investigated. The air concentrations of lead at worksites were 0.25 to 42.5 mg/m3. The geometric means of PbB, PbU and delta-ALAU in lead exposed group were 40.03 micrograms/dl, 71 micrograms/l and 4.68 mg/l respectively, which were significantly higher (P less than 0.001) than those (7.01 micrograms/dl, 6.0 micrograms/l and 1.81 mg/l respectively) in the reference group. There were no clinical symptoms or signs of nerve damage in either group. Alcoholism and diabetes were excluded in both groups. Nerve conduction velocity was measured by a DISA 1500 electromyograph in both groups. Eleven electroneurographic parameters, including motor nerve conduction velocity (MCV) and distal latency (DML) of median, ulnar and peroneal nerves as well as sensory nerve conduction velocity (SCV) and distal latency (DSL) of median, ulnar and sural nerves, showed statistically significant differences between the two groups. However, the results of electroneurographic measurements of each individual in the lead-exposed group were all within the normal range. There was no correlation between the blood-lead levels and the neurophysiological measurements except for the median MCV. No correlation was seen between the median MCV and the exposure duration.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurophysiological approaches to the detection of early neurotoxicity in humans

Various neurophysiological methods, including electroencephalography, electromyography, nerve conduction velocities, and evoked potential techniques, have been used to detect early signs of neurotoxicity in humans. These methods have been applied to groups of occupationally exposed workers and their referents in epidemiologic studies, to patients with suspected or proven diseases after long-term work in toxic environment, and to human subjects during or after experimental exposure. The main body of knowledge arises from epidemiologic studies of occupationally exposed subjects, and several chemicals widely used in industry have been shown to be neurotoxic. Of these, e.g., lead causing peripheral neuropathy, some solvents like carbon disulfide, n-hexane, and methyl n-butyl ketone also causing neuropathy and at times central nervous system effects as well as acryl amide have been studied using neurophysiological approaches. Several other solvents including toluene, xylene, and various mixtures of organic solvents have been suspected to be neurotoxic, and nervous system effects have been ascribed to those in several neurophysiological studies. Some studies have elucidated acute nervous system effects of ethyl alcohol or industrial solvents in experimental situations applying, for example, evoked potential techniques or electroencephalography.