ブロム酸塩による内耳障害に関する臨床的ならびに実験的研究

抄録

Potassium bromate and sodium bromate are generally used as the neutralizing mediums in the cold wave permanent process. Poisoning due to the ingestion of these substances, by children accidentally or by adults for suicide, is not rarely encountered and up to date twenty-seven case reports have come to the author's attention. The ingestion of bromate causes the gastrointestinal irritability, renal damage with uremia and severe hearing loss.
Case Report
Two patients who had history of bromate ingestion visited our clinic complaining hearing loss. Hearing test of the first patient revealed a total deafness, and the second case revealed a severe perceptive deafness with recruitment phenomenon. The disorders of the vestibular function were not found in both patients. From the clinical findings of the patients it was suspected that hearing loss due to bromate poisoning is caused by the lesion in the auditory part of the labyrinth.
Experimental Studies
In order to clarify the mechanism of the hearing loss in bromate poisoning, the electro-physiological and histochemical studies were performed in guinea pigs.
Methods: Cochlear microphonics (CM) were recorded with differential electrode technique. Endocochlear DC potential (EP) and negative DC potential of Corti's organ were measured with a glass pipette microelectrode via the round window membrane. The changes of potentials were observed for several hours after subcutaneous injection of sodium bromate. After the recording of CM or EP and negative DC potential of Corti's organ was finished, the succinic dehydrogenase staining was performed in vivo and the surface specimens of the cochlea were prepared. The kidneys of the animal were removed and stained with hematoxylin and eosin for microscopic examination.
Results: A-group receiving 100mg/kg of sodium bromate. Twenty-four hours after the injection, four animals out of twenty lost Preyer's reflex. In these animals CM could not be evoked even with intense sound and EP showed 0mV. In the histochemical observation of these animals, a marked decrease of enzymatic activity and cellular destruction of the outer hair cells were found, but the inner hair cells were still observed with a slight decrease of enzymatic activity. Histological examination of the kidneys revealed hyaline droplet degeneration, cloudy swelling and necrosis of the epithelial cells in renal tubules, especially in proximal convoluted tubules, but the glomeruli remained unchanged.
B-group receiving 200mg/kg of sodium bromate. CM began to decrease about one hour after the injection and reached to noise level within four hours. EP showed a reduction almost similar to that of CM and reached to 0mV within three hours. Negative DC potential of the Corti's organ showed frequently a tendency to decrease near 0mV. Histochemically no changes were found in the surface specimens within three hours after the injection, although a slight decrease of enzymatic activity and swelling of cells were observed later in the outer hair cells. A remarkable decrease of enzymatic activity and the severe destruction of the outer hair cells were observed six hours after the injection. The histological findings of the kidneys were similar to that of animals received 100mg/kg of sodium bromate.
Conclusions
1. The ingestion of a large quantity of bromates causes severe hearing loss with positive recruitment phenomenon.
2. The vestibular function is not injured by bromate.
3. Cochlear microphonics, endocochlear DC potential and negative DC potential of Corti's organ decreased equally after the injection of bromate. Histochemical examination of the cochlea revealed the degenerative changes of the outer hair cells.
4. Hearing loss in bromate poisoning is attended by the lesions of renal tubules, especially prominent in proximal convoluted tubules.
5. Hearing loss in bromate poisoning is caused by the lesions of the stria vascularis and the outer hair cells.