[Chronic and predominantly sensory polyneuropathy in Toroku Valley where a mining company produced arsenic]

We report 9 patients (5 males, 4 females, ages 63-77) with chronic polyneuropathy. They were exposed to arsenic for about 15-40 years in Toroku Valley, Takachiho-Town, Miyazaki Prefecture, Japan, where a mining company produced arsenic from 1920-1962. Predominantly sensory polyneuropathy was the most significant neurological finding. In 5 of them, superficial and deep sensation was equally affected over the entire body, including head, face, and mucous membranes of the mouth. The corneal reflexes were absent or sluggish. Pin-prick and light-touch perception was absent in their hands and legs. Another sensory disorder such as glove and stocking-type was seen in 4 of them. All 9 patients were comfortable with extremely hot water in their beverages, their baths, and their wash basins compared with controls. But these patients felt that their temperature sensation was normal. Motor involvement was minimal. Although motor-nerve conduction velocities were normal or reduced minimally, sensory-nerve conduction velocities were moderately reduced. Sural-nerve biopsy revealed reduction of both small myelinated and unmyelinated fibers, which occurs with axonal degeneration of peripheral nerves. Other main symptoms and signs were tension-type headaches, non-painful tonic spasms of limbs, and losses or significantly decreased sensations of taste and smell. Dantrolene-sodium was effective for the treatment of their non-painful tonic spasms of limbs. As for the general medical condition of these patients, all of them had suffered from chronic bronchitis and skin eruption during childhood or in their early life or in their young adulthood when the mine was producing arsenic. At the time of this study only four of them suffered from chronic bronchitis and none of them had skin eruptions or discoloration of the skin, 37 years after closure of the mine. These 9 patients were diagnosed as having chronic arsenic poisoning and arsenic polyneuropathy. The multiplicity of symptoms found in these patients--anosmia, ageusia, chronic bronchitis, tension-type headaches, and non-painful tonic spasms of limbs--differs from the symptoms previously reported cases with arsenic poisoning. This may be due to combined overexposure to environmentally hazardous arsenic by effluent gas, dust, and drinking water in Toroku Valley. As concerns the sensory disorders described above, it is necessary to investigate sensory conduction pathways, including cerebral sensory cortex, spinal cord, and skin sensory receptors such as Pacini corpuscles, and Meissner corpuscles. Unfortunately, no information has been obtained about this problem because there were no autopsy cases.