High-Tone Loss in Otosclerosis

Abstract

The hearing loss in otosclerosis follows certain fairly typical lines. At the early stage the loss is often greatest at the low frequencies. According to the impedance formula of Johansen, this is due to stiffness of the ossicular chain. Later, when the stapes footplate has become fixed to the oval window, the audiograms show mass flattening; hearing now deteriorates also in the high-frequency range, the final result being a more or less even impairment throughout the auditory range. Yet, as we all know, audiograms indicating greater hearing loss in the high than in the low range are not infrequent in patients with otosclerosis. The air-bone gap—always great in these cases at the low frequencies—is reduced towards the high frequencies, and in some cases the air and bone audiograms may even unite. This results in a curve of mixed deafness type, attributed to a cochlear involvement complicating a purely conductive lesion.