Prevalence of dead regions in subjects with sensorineural hearing loss

To estimate the prevalence of dead regions in adult subjects with sensorineural hearing impairment as a function of audiometric threshold and frequency and to assess the extent to which the presence/absence of a dead region can be predicted from the audiogram, gender, or age.

Data were obtained from a random sample of adults attending an audiology clinic in Mysore, India. Audiometric air and bone conduction thresholds and tympanometry were used to identify 317 subjects (592 ears) with sensorineural hearing loss. Their ages ranged from 17 to 95 yr (mean = 57 yr). The threshold-equalizing noise hearing level (TEN (HL)) test, administered using the TEN(HL)-test CD and an audiometer, was used to determine the presence or absence of dead regions in these subjects for test frequencies ranging from 0.5 to 4 kHz. Nine subjects had to be excluded as the absolute thresholds were too high for the TEN(HL) test to be administered. Of the remaining 308 subjects (556 ears), 209 (68%) were male and 99 (32%) were female. The hearing losses ranged from mild to severe.

Results are presented only for frequencies and ears for which the TEN level could be made high enough to produce at least 10 dB of masking. Classifying by subject, 177 (57.4%) were found to have a dead region in one or both ears for at least one frequency. Fifty-four women (54.5%) and 123 men (58.8%) had dead regions in one or both ears. Classifying by ear, 256 (46%) were diagnosed as having a dead region at one frequency or more: 233 ears (41.9%) had only a high-frequency dead region, 13 ears (2.3%) had only a low-frequency dead region, and 10 ears (1.8%) had a dead region at both low and high frequencies, with a surviving middle-frequency region. It was not possible to achieve both high sensitivity and high specificity when attempting to predict the presence/absence of a dead region from the audiogram. However, for each test frequency, 59% or more of ears had a dead region when the absolute threshold was above 70 dB HL. A very steep slope of the audiogram is suggestive of a high-frequency dead region but does not provide a reliable diagnostic method. Chi-square tests indicated that the prevalence of dead regions did not vary significantly with age or gender.

The results indicate a relatively high prevalence of dead regions in adults with sensorineural hearing impairment, especially for frequencies at which the hearing loss exceeds 70 dB HL.