機能性難聴における持続音と断続音の域値差

Abstract

A simple yet reliable easy screening method for functional hearing loss was developed using an air conduction pure-tone audiometer.We performed pure-tone audiometry in 440 ears from 220 patients (101 males, 119 females) using 7 continuous and 7 pulse pure tones at 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz and 8000 Hz. The hearing thresholds measured by continuous tones were compared with those measured by pulse tones at each frequency, and the number of frequencies which showed a 10 dB or greater threshold improvement or deterioration were counted.Of the 440 ears, 130 ears were diagnosed with sensorineural hearing loss of unknown origin, 51 ears with functional hearing loss, 48 ears with normal hearing, 39 ears with congenital sensorineural hearing loss, 29 ears with presbycusis and 22 ears with occupational noise deafness or others. A comparison of the hearing thresholds in the 440 ears revealed greater than 1 out of 7 frequencies threshold improvements in 48 ears (10.9%), greater than 1 out of 7 frequency deterioration in 30 ears (6.8%), and only one or no frequency threshold differences in 362 ears (82.3%). In the 48 ears with improved thresholds, 38 ears (79.2%) were diagnosed with functional hearing loss. Moreover, 27 ears (6.1%) out of the 440 ears showed over 4 frequencies threshold improvements, and all of these ears were diagnosed with functional hearing loss.These results suggest that this novel method, comparing the thresholds measured by continuous versus pulse tones, was useful for the simple screening of functional hearing loss. If a threshold improvement using a continuous tone is observed in more than 1 frequency, then functional hearing loss should be suspected, and threshold improvements in more than 4 frequencies are even more likely to indicate functional hearing loss. For further accurate diagnosis, Bekesy audiometry and auditory brain stem evoked responses are useful.