title: Auditory efferent dysfunction in normal-hearing chronic idiopathic tinnitus.
abstract: OBJECTIVE
  To investigate the function of the auditory efferent system in patients with chronic idiopathic tinnitus, but normal pure-tone audiograms.
  
  
  METHODS
  We studied 15 subjects with normal hearing that had experienced either unilateral or bilateral persistent tinnitus for at least 3 months. The ears of the 15 subjects were classified into tinnitus-positive-ear (TPE) and tinnitus-negative-ear (TNE) groups. The control-ear group (CE) comprised the ears of 15 subjects with normal hearing and no tinnitus. We measured different types of otoacoustic emissions (OAEs), including spontaneous (SOAEs), transient evoked (TEOAEs), and distortion product (DPOAEs). We also analyzed contralateral suppression of OAEs and auditory brainstem responses (ABRs). Data were compared among TPE, TNE, and CE groups.
  
  
  RESULTS
  The data associated with cochlear mechanics, including the prevalence of SOAEs, the number of SOAE peaks, and the overall TEOAE responses in the absence of a contralateral stimulus, were not significantly different among the TPE, TNE, and CE groups. In the TPE group, contralateral stimuli failed to significantly suppress overall TEOAEs, and contralateral suppression of DPOAEs was significantly reduced over a limited frequency range. Furthermore, the TPE group showed prolonged latencies in waves III and V of ABRs.
  
  
  CONCLUSIONS
  This study demonstrated that abnormal contralateral suppression of OAEs and ABRs indicated a dysfunction in the ipsilateral efferent medial olivocochlear system; this might play a role in normal-hearing tinnitus.
authors.affiliation: Department of Otolaryngology, Cathay General Hospital, Taipei, Taiwan.
authors.forename: S Y
authors.initials: SY
authors.lastname: Hsu
authors.forename: P C
authors.initials: PC
authors.lastname: Wang
authors.forename: T H
authors.initials: TH
authors.lastname: Yang
authors.forename: T F
authors.initials: TF
authors.lastname: Lin
authors.forename: S H
authors.initials: SH
authors.lastname: Hsu
authors.forename: C J
authors.initials: CJ
authors.lastname: Hsu
mesh_terms: D000328:Adult; D002908:Chronic Disease; D004525:Efferent Pathways / Q000502:physiology; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017084:Otoacoustic Emissions, Spontaneous / Q000502:physiology*; D014012:Tinnitus / Q000503:physiopathology*