Ceranic, Borka; (1999) Objective assessment of tinnitus: The role of cochlear emissions. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Tinnitus is a subjective phenomenon, which remains poorly understood with respect to the underlying mechanism. At present, no objective method for assessment is available. The subject of this thesis is to assess the role of cochlear emissions in objective evaluation of tinnitus. There is evidence of a bi-directional interaction between the cochlea and the central auditory system, and, assuming that tinnitus is a consequence of altered neural activity due to a lesion or dysfunction at any level in the auditory system, the alteration may be reflected in cochlear mechanics, and therefore, otoacoustic emissions (OAEs). Cochlear mechanics have been examined in different groups of patients with tinnitus, homogeneous with respect to auditory pathology and/or audiometric thresholds: (i) normal hearing and tinnitus subsequent to presumed central nervous system pathology consequent upon head injury (ii) those with normal hearing and no identifiable pathology (iii) those with tinnitus following noise exposure and (iv) Menière's disease. Four separate studies, examining each of these groups, form the integral part of the thesis. The fifth study, including all groups, explored a unique form of spontaneous (mechanical) activity in the cochlea. OAE were recorded using standard techniques, suitable for the clinical environment, with the Otodynamics ILO88/92 Analyser; Transient click-evoked (TEOAEs) and spontaneous otoacoustic emissions (SOAEs), in order to assess the structural and functional state of the cochlea, and TEOAEs under contralateral acoustic stimulation to assess the function of the medial olivo-cochlear system. Studying OAEs in different, but aetiologically homogenous, groups of patients with tinnitus has enabled the identification of group-characteristics, consequent upon the particular underlying mechanisms, in the generation of tinnitus. In significant number of patients, an increased variability of SOAEs associated with the complaint of tinnitus, has been observed. There is evidence to suggest that changes in cochlear mechanics in patients with tinnitus have resulted from dysfunction of efferent control, and reflect hyperexcitability in the auditory pathways.

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