Objective: This study aimed to clarify the reasons why clinical otosclerosis, a very common disease among Caucasians, is not prevalent among Japanese.
Study design: The incidence, site, activity, and volume of otosclerotic foci were examined in 1011 temporal bone sections from 507 Japanese individuals.
Setting: This study was prepared at the temporal bone laboratory, Fukushima Medical University, Fukushima.
Results: Otosclerotic foci were observed in 2.56% of individuals and in 1.48% of the ears. The most common site of involvement was anterior to the oval window region, but this was only in 38.9% of the ears with otosclerotic foci. The otosclerotic foci were not involved in the stapediovestibular articulation or the endosteal layer of the otic capsule in any ears. An active change of the otosclerotic focus was seen in 33.3% of ears with otosclerosis. The volume of otosclerotic foci at the site anterior to the oval window region was less than 0.8 mm3 in 5 out of 7 ears.
Conclusion: The incidence of histologic otosclerosis among Japanese seemed to be almost the same as that among Caucasians. Three reasons why clinical otosclerosis was not as prevalent among Japanese as among Caucasians are suggested: low incidence of involvement of foci anterior to the oval window, low activity, and small lesion without involvement of the footplate and/or membranous labyrinth of the inner ear.