Neurophysiological evidence of methylmercury neurotoxicity.

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.