Application of the TEN test to hearing-impaired teenagers with severe-to-profound hearing loss.

Hearing impairment is often associated with damage to the hair cells of the cochlea. An area of the cochlea with complete loss of function of inner hair cells is known as a 'dead region'. Dead regions can be identified by measuring detection thresholds for pure tones in quiet and in threshold-equalizing noise (TEN). So far, the TEN test has only been used to identify dead regions in adults with moderate-to-severe hearing impairment. The aim of this study was to assess problems in applying the TEN test to teenagers with longstanding severe-to-profound sensorineural hearing impairment, and to assess the prevalence of dead regions in this population. The subjects had a mean age of 14 years, and there were 13 females and 20 males. The stimuli for the TEN test were derived from a CD, whose output was routed via a GSI-16 audiometer and an amplifier to Sennheiser HD580 earphones. For each ear of each subject, both absolute thresholds and masked thresholds in the TEN were measured. For the majority of ears, the results were in-conclusive at some frequencies, due to the maximum output of the audiometer being reached when measuring the absolute or masked threshold. In almost all cases, the diagnosis was uncertain at some frequencies because the TEN could not be made sufficiently intense to produce significant masking. However, for 23 (70%) subjects, the criteria for a dead region at medium or high frequencies were met in at least one ear. For eight (35%) of these subjects, the criteria were only just met. Sixteen of the 24 subjects with a congenital hearing impairment, and four of the five subjects with an acquired impairment, met the criteria for a dead region. The results suggest that dead regions are relatively common among teenagers with a longstanding hearing impairment.