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Neurophysiological evidence of methylmercury neurotoxicity
Katsuyuki Murata1, Philippe Grandjean, Miwako Dakeishi
1Department of Environmental Health Sciences, Akita University School of Medicine, Akita, Japan. winestem@med.akita-u.ac.jp
Background:
A variety of neurophysiological measures are useful in hospital settings for diagnostic and other clinical purposes. Previously, abnormal changes in various sensory evoked potentials (EPs), and heart rate variability (HRV) were observed in patients with acquired and fetal Minamata disease (MD; methylmercury poisoning). In recent years, some of these methods have been used for the risk assessment of low-level methylmercury exposure in asymptomatic children. The objectives of this article were to present an overview of neurophysiological findings involved in methylmercury neurotoxicity and to examine the usefulness of those measures.
Methods:
The reports addressing both neurophysiological measures and methylmercury exposure in humans were identified and evaluated.
Results:
The neurological signs and symptoms of MD included paresthesias, constriction of visual fields, impairment of hearing and speech, mental disturbances, excessive sweating, and hypersalivation. Neuropathological lesions involved visual, auditory, and post- and pre-central cortex areas. Neurophysiological changes involved in methylmercury, as assessed by EPs and HRV, were found to be in accordance with both clinical and neuropathological observations in patients with MD.
Conclusions:
EPs and HRV appear to be useful and objective methods for assessing methylmercury neurotoxicity. However, subtle changes due to low-level methylmercury exposure may not necessarily be of clinical relevance, and interpretation of small deviations from expectations must be cautious.
Insights
Evoked potentials (EPs) and heart rate variability (HRV) can objectively assess methylmercury neurotoxicity. Caution is advised when interpreting subtle changes from low-level exposure in children.
Area of Science:
- Neuroscience
- Toxicology
- Environmental Health
Background:
- Neurophysiological measures like evoked potentials (EPs) and heart rate variability (HRV) are used clinically.
- Abnormal EPs and HRV were previously noted in Minamata disease (MD), caused by methylmercury poisoning.
- These methods are now being explored for assessing low-level methylmercury exposure in children.
Purpose of the Study:
- To provide an overview of neurophysiological findings related to methylmercury neurotoxicity.
- To evaluate the utility of neurophysiological measures for assessing methylmercury exposure and toxicity.
Main Methods:
- Literature review of human studies involving neurophysiological measures and methylmercury exposure.
- Evaluation of identified reports to synthesize findings.
Main Results:
- Neurological symptoms of MD include sensory and cognitive impairments.
- Neuropathological findings in MD affect sensory cortex areas.
- Neurophysiological changes (EPs, HRV) in MD align with clinical and pathological observations.
Conclusions:
- Evoked potentials (EPs) and heart rate variability (HRV) are valuable objective tools for assessing methylmercury neurotoxicity.
- Subtle neurophysiological changes from low-level methylmercury exposure may lack clinical significance.
- Careful interpretation is necessary when assessing minor deviations in neurophysiological measures.
