Clinical Symptoms, Neurological Signs, and Electrophysiological Findings in Surviving Residents with Probable Arsenic Exposure in Toroku, Japan

Abstract

Chronic arsenic intoxication is known to cause multisystem impairment and is still a major threat to public health in many countries. In Toroku, a small village in Japan, arsenic mines operated from 1920 to 1962, and residents suffered serious sequelae of arsenic intoxication. We have performed annual medical examinations of these residents since 1974, allowing us to characterize participants' long-term health following their last exposure to arsenic. The participants could not be described as having "chronic arsenic intoxication," because their blood arsenic levels were not measured. In this study, we defined them as having "probable arsenic intoxication." Symptoms frequently involved the sensory nervous system, skin, and upper respiratory system (89.1-97.8%). In an analysis of neurological findings, sensory neuropathy was common, and more than half of the participants complained of hearing impairment. Longitudinal assessment with neurological examinations and nerve conduction studies revealed that sensory dysfunction gradually worsened, even after exposure cessation. However, we could not conclude that arsenic caused the long-term decline of sensory function due to a lack of comparisons with age-matched healthy controls. This is the first study to characterize the longitudinal sequelae after probable arsenic exposure. Our study will be helpful to assess the prognosis of patients worldwide who still suffer from chronic arsenic intoxication.

Fig. 1

Nerve conduction studies of the upper and lower limbs. In the upper extremities, the compound muscle action potential (CMAP) of the median motor nerve and the nerve conduction velocity (NCV) of the median sensory nerve were significantly worsened. In the lower extremities, the CMAP of the tibial motor nerve deteriorated while the NCV of the sural sensory nerve was significantly ameliorated. NCV nerve conduction velocity, CMAP compound muscle action potential, SNAP sensory nerve action potential