International Congress on Newborn Hearing Screening, Diagnosis and Intervention (NHS) location:Como, Italy date:May 27 29/05/2004
As a consequence of the successful hearing screening program in Flanders, the need for accurate objective diagnostics has increased. The aim of this study was to report on clinical experience using dichotic multiple-stimulus auditory steady-state responses (ASSR) as an objective technique to estimate frequency-specific hearing thresholds in hearing-impaired infants. ASSRs were evoked by 100% amplitude-modulated and 20% frequency-modulated tones with carrier frequencies of 0.5, 1, 2 and 4 kHz and modulation frequencies ranging from 82 to 110 Hz. Eight signals (four to each ear) were presented simultaneously through insert earphones. Tests were carried out in a soundproof room. A first group of 20 infants between 3 months and 5 years old was tested under general anaesthesia. This was a group of difficult-to-test children. ASSR recordings were combined with click-evoked ABR measurements. Behavioural hearing thresholds were defined in later test sessions as soon as possible after the ASSR test, dependent on medical and developmental factors. A second group of 15 babies was tested in natural sleep. These babies were between 2 weeks and 5 months old and were referred after a failed hearing screening carried out in the neonatal intensive care unit. A comparison was made between the ASSR, the ABR and behavioural hearing thresholds. Threshold comparisons, test duration and feasibility of testing in natural sleep will be discussed at the conference. The results indicate that multiple-frequency ASSRs offer the possibility to accurately estimate frequency-specific hearing thresholds in babies in a time-efficient way.