Audiometric Pattern and Speech Discrimination in Sensorineural Hearing Loss

Abstract

Correlations were made between audiometric pattern (especially flat and gradual high tone loss)and speech discrimination score (SDS) in 255 ears with sensorineural hearing loss that were tested at the Department of Otolaryngology of Shirakawa Kousei General Hospital during the past 6 years.
First, the audiometric pattern was defined on all frequencies (0.125 k-8 kHz). SDS of each audiometric pattern resembled that in all similarly affected ears, but in younger ears (under 75 years old, the average value of pure tone hearing level subtracted from speech reception threshold was under 10 dB), SDS of patients with flat audiogram or abrupt high tone loss (mainly 8 kHz) maintained a good score (over 70%) at 10 dB intervals below 70 dB, then sharply decreased at 70 dB. However, SDS of patients with gradual high tone loss decreased in proportion to hearing loss. This fact supports Schuknecht's classification of hearing loss in presbycusis. Furthermore, this suggests that there is a boundary of good SDS at the 60 dB level, at which SDS was marked by deafness and a flat audiometric pattern caused by atrophy of the stria vascularis.
Second, the audiometric pattern was defined by the slope of the audiogram (value of 2 kHz loss subtracted from 0.5 kHz loss, and 4 kHz loss from 0.5 kHz loss). The gradual high tone loss group had a good SDS (over 70%) under 50 dB. In cases involving hearing loss reaching and exceeding 50 dB, SDS declined abruptly. Good SDS almost disappeared and poor SDS (under 50%) increased suddenly. This suggests that not only that the decrease in neurons reached the minimum necessary to maintain a good SDS, but also that the neurons which transfer information under 50 dB exerted great influence on SDS.
Differences were analyzed, between each audiometric pattern and between the group before abrupt deccrease in SDS and the group after the abrupt decrease in the flat audiogram or gradual high tone loss group.