Comparison of auditory steady state response among normal hearers and patients with different degrees of sensorineural hearing loss

ABSTRACT

50 adult subjects [100 ears], with a mean age of 33.47 years +/- 10.53 ranging from 18 to 70 years, were enrolled in this study. Ears were divided into 7 groups according to the degree of hearing obtained by pure tone audiometry [PTA]. Auditory steady state response [ASSR] was done for all groups by means of the MASTER biologic. To study the ASSR among normal individuals and patients with different degrees of sensorineural hearing loss [SNHL] and find out the ASSR and behavioural threshold difference in these groups. There was no statistically significant difference among the groups as regards age or gender [p>0.05]. There was a statistically significant difference [p<0.05] among the groups as regards the mean PTA-ASSR hearing threshold difference at all frequencies. The difference decreased as the degree of hearing loss increased [the mean hearing threshold level obtained by ASSR approaches that obtained by PTA] at severer degrees of SNHL [at groups 5, 6 and 7]. The behavioural thresholds obtained by PTA and physiologic thresholds obtained by ASSR were highly correlated. The relationships were described by the following equations Average PTA = -25.76 + [1.11 x Average ASSR] and according to the frequencies, at 500 Hz PTA= -22.77 + [1.02xASSR]; at 1000 Hz PTA= -21.30 + [1.03xASSR]; at 2000 Hz PTA= -14.58 + [0.99xASSR] and at 4000 Hz PTA= -14.50 + [0.98xASSR]. ASSR threshold does not reflect the PTA threshold reliably in normal hearers and in milder degrees of SNHL. And ASSR threshold reflects PTA threshold more reliably at severer degrees of SNHL especially at mid frequencies [1000 and 2000 Hz]. So we recommend using ASSR as an additional objective method in estimating the behavioural threshold at moderately severe, severe and profound SNHL with attention in estimating the hearing threshold by ASSR in normal hearing and in slight, mild and moderate degrees of SNHL