title: Auditory steady-state responses to bone conduction stimuli in children with hearing loss.
abstract: OBJECTIVE
  The auditory steady-state response (ASSR) to air-conduction (AC) stimuli has been widely incorporated into audiological test-batteries for the pediatric population. The current understanding of ASSR to bone conduction (BC) stimuli, however, is more limited, especially in the case of infants and children. There are few reports on ASSR thresholds to BC stimuli in infants and young children, and none for infants or children with hearing loss. The objective of this study was to investigate BC ASSR thresholds in young children with normal hearing and various types and degrees of hearing loss.
  
  
  METHODS
  AC and BC ASSR thresholds are reported for 48 young children (mean age+/-SD=2.8+/-1.9 years; age range=0.25-11.5 years; 23 female). Hearing status was classified by assessing all children with a comprehensive test battery including tympanometry, diagnostic distortion-product otoacoustic emissions, click-evoked AC auditory brainstem response, AC and BC ASSR thresholds, and an otologic examination. The subjects were assigned to the categories normal hearing, conductive loss, and sensorineural loss (mild-to-moderate or severe-to-profound), for group analysis. AC and BC ASSR stimuli (carrier frequencies: 0.25-4 kHz; 67-95 Hz modulation rates; 100% amplitude and 10% frequency modulated) were presented using the GSI Audera system.
  
  
  RESULTS
  Minimum levels at which spurious BC ASSR occur were established in the group of children with severe-to-profound sensorineural hearing loss (25, 40, 60, 60 and 60 dB for 0.25, 0.5, 1, 2, and 4 kHz, respectively). Children with normal hearing presented mean (1 SD) BC ASSR thresholds of 19 (9), 18 (7), 16 (11), 24 (7), and 26 (8) dB HL at 0.25, 0.5, 1, 2, and 4 kHz, respectively. Significantly lower thresholds (p<0.0001) were obtained for 0.25, 0.5 and 1 kHz than for 2 and 4 kHz. At 0.25 kHz, 39% of thresholds were at the minimum level of spurious response occurrence. More than half (54%) of the BC thresholds in the group with mild-to-moderate sensorineural hearing loss were recorded at or above the minimum levels at which spurious response occurred. In children with conductive hearing loss, the average BC ASSR thresholds corresponded closely to those in the normal hearing group except at 1 kHz and revealed an air-bone gap.
  
  
  CONCLUSIONS
  Spurious bone conduction ASSR responses limit the intensity range for which the technique may be employed in infants and children, especially at lower frequencies. Consequently, the 0.25 kHz stimulus is not recommended for clinical use. In infants and young children, sensorineural hearing loss of a moderate or greater degree in the high frequencies (1-4 kHz), and of a mild or greater degree in the low frequencies (0.5 kHz), cannot be quantified using BC ASSR. This is due to the presence of the stimulus artifact. In cases of conductive hearing loss, BC ASSR can effectively quantify sensory hearing between 0.5 and 4 kHz, but interpretations must be made cautiously within the limitations of stimulus artifact occurrence across frequencies.
authors.affiliation: Department of Communication Pathology, University of Pretoria, Pretoria 0002, South Africa. dewet.swanepoel@up.ac.za
authors.forename: De Wet
authors.initials: de W
authors.lastname: Swanepoel
authors.forename: Shamim
authors.initials: S
authors.lastname: Ebrahim
authors.forename: Peter
authors.initials: P
authors.lastname: Friedland
authors.forename: Andre
authors.initials: A
authors.lastname: Swanepoel
authors.forename: Lidia
authors.initials: L
authors.lastname: Pottas
mesh_terms: D000158:Acoustic Impedance Tests; D000161:Acoustic Stimulation / Q000379:methods*; D001309:Auditory Threshold / Q000502:physiology; D001844:Bone Conduction / Q000502:physiology*; D002648:Child; D002675:Child, Preschool; D005072:Evoked Potentials, Auditory / Q000502:physiology; D005260:Female; D006314:Hearing Loss, Conductive / Q000503:physiopathology*; D006319:Hearing Loss, Sensorineural / Q000503:physiopathology*; D006801:Humans; D007223:Infant; D008297:Male; D012720:Severity of Illness Index