The Localization of Hearing Impairment in Athetoids

Abstract

Introduction

The occurrence of hearing loss associated with athetosis has been known for some time. It has been demonstrated that the hearing impairment is of the perceptive type. The pathophysiology responsible for the hearing deficiency has been a subject of conjecture, and the site of the lesion has been a source of some speculation. The preponderance of opinion concerning this latter point seems to have been in favor of its being a retrocochlear involvement.

The preponderance of opinion concerning the perceptive type of hearing loss found in athetoids is that it is due to retrocochlear damage, probably as a concomitant to the central system damage which caused their physical disability. If this is so, then such athetoids might be expected to respond in atypical ways to a battery of audiologic tests which are sensitive to the detection of perceptive type hearing loss with cochlear involvement.

Ten Norwegian athetoids, 11 to 28 years of age, with physical involvement which ranged from slight to severe, and who had had negative otological findings, were tested. Air and bone conduction pure tone audiometric examinations were made. Tests of monaural and binaural recruitment, aural harmonics threshold, tolerance range, and speech reception tests using phonetically balanced material were given to each subject. In addition, signs of diplacusis, and an idiophonic effect were noted.

Each of the subjects showed perceptive type hearing loss, more noticeable in the high frequencies. Every case showed signs of cochlear involvement. All were found to have loudness recruitment. All reported hearing the beats in the test of aural harmonics at a point which was lower than that found in unimpaired ears. Responses to the phonetically balanced material of the speech reception testing were varied, but as a whole, correlation between the extent of hearing loss for high frequencies and speech discrimination was fairly close. The majority of the subjects showed intolerance for sounds at high intensity. In some cases, diplacusis was reported by the subjects, and in others an idiophonic effect was noted in connection with the testing of aural harmonics. On the basis of the outcome of the testing, it was concluded that their hearing loss is of cochlear origin. This is contrary to the majority of opinions expressed by others, but it is a fact derived from experimental research. Previous studies have not included as extensive a battery of audiologic tests.

Seeking an explanation for such signs of cochlear involvement in these athetoids, the possibility of oxygen deprivation as the causative factor is discussed.