Auditory steady-state responses in babies with normal hearing and with temporary conductive hearing loss

Abstract

Abstract Objectives: To investigate whether test age and middle ear dysfunction had a significant effect on the variability of Auditory Steady-State Response (ASSR) thresholds when this test was undertaken on referrals from the newborn hearing screen. Methods: ASSR thresholds were measured at octave intervals from 500 Hz to 4000 Hz. They were recorded in 389 ears with normal hearing and middle ear function, and in a further 189 ears with temporary middle ear dysfunction. The modal corrected age at which the tests were undertaken was four weeks, with a minimum of one week and maximum corrected age of 26 weeks. Results: The mean ASSR thresholds of those with normal hearing were 47dB HL at 500 Hz, 36dB HL at 1000 Hz, and 34dB HL at both 2000 Hz and 4000 Hz. Standard deviations (SDs) from the mean ranged from 7.7 to 9.9dB. For those with middle ear dysfunction the mean ASSR thresholds were significantly greater at each frequency, with thresholds of 65dB HL at 500 Hz, 55dB HL at 1000 Hz, 53dB HL at 2000 Hz and 52dB HL at 4000 Hz. SDs from the mean ranged from 12.9 to 17.9dB. Mean thresholds decreased at all frequencies during the first half of infancy. In those with normal middle ear function the decrease was only 2dB at 500 Hz, but was over 5dB at both 1000 and 2000 Hz and was 4dB at 4000 Hz. A similar decrease was seen over the same period in those with middle ear dysfunction. Conclusions: ASSR thresholds measured in early infancy are affected by both test age and the presence of middle ear dysfunction and are more variable than ABR thresholds measured in babies with normal hearing or a mild conductive loss. A flexible test battery for gaining frequency specific information is therefore required at this age.