Incidence and characteristics of otosclerosis in the Japanese population

Objective: Otosclerosis is thought to be quite an uncommon disease in Japan. However, in recent years the incidence of this disease seems to have increased. Here we report about the characteristics and incidence of this disease in the Japanese population who underwent stapes surgery in our department. Methods: A total of 80 patients (115 ears), who underwent stapes surgery by a single surgeon in 21 years and 8 months were included in this study. Results: The incidence of clinical otosclerosis was found to be 0.22% among the outpatients with ear disease. During the first half of the period, the ratio of stapes surgery/tympanoplasty was less than 0.05. While, during the second half of this period, this ratio had increased to 0.08. The average number of stapes surgery performed in the first half period was 3.7 ears/year, and that in the second half was 6.8 ears/year. In contrast to otosclerosis in Caucasians, pure tone threshold in lower frequencies was much higher than that of higher frequencies (except for 8000 Hz). However, the improvement of the threshold after surgery was not so different from that reported in Caucasians. Conclusions: Taken together, the present results clearly demonstrate that the incidence of otosclerosis in Japan has been increasing. Moreover the rise in the slope of the conduction curve at higher frequencies may be a reflection of the pathological characteristics of otosclerosis in Japanese population, which is less invasive and has limited otosclerotic foci in the temporal bone.