DISTORTION PRODUCT OTOACOUSTIC EMISSIONS AND EXTENDED HIGH-FREQUENCY (EHF) AUDIOMETRY IN NORMAL-HEARING PATIENTS WITH UNILATERAL TINNITUS

Fabijanska A (1),  Smurzynski J (2), Kochanek K (1), Skarzynski H (1).

(1) Institute of Physiology and Pathology of Hearing, Warsaw, Poland; (2) Department of Communicative Disorders, East Tennessee State University, Johnson City, TN, U.S.A.

It has been suggested that the presence of a limited area of damaged outer hair cells (OHCs) with intact inner hair cells, which may not be detected on the conventional audiogram, results in unbalanced neural activity between Type I and Type II fibers leading to tinnitus. In normal-hearing tinnitus patients, DPOAEs provided ambiguous data of OHC function when compared to non-tinnitus controls. Hearing loss in the EHF region may decrease DPOAEs evoked at lower frequencies. Results of EHF audiometry in tinnitus patients are limited. The aim of the study was to evaluate DPOAEs and EHF thresholds in normal-hearing patients reporting unilateral tinnitus in left ear. Thus, each subject acted as their own control.

Data were obtained for 31 subjects with bilateral hearing thresholds <25 dB HL from 0.25 to 8 kHz and <70 dB HL at 10, 12.5, 14, and 16 kHz. The DP-grams were measured in the 0.5-8 kHz range using 65/55-dB SPL primaries and f2/f1=1.2. The data analyses included DPOAEs with S/N>3 dB.

The signed rank test showed that audiometric thresholds in the left ears were significantly higher than those in the right ears at all four EHFs. Mean DPOAE levels of the left ears were lower than those of the right ears for all primaries, except for the 500-Hz frequency region. A paired-comparison test of DPOAE levels of each patient’s right and left ear revealed significant differences at 6 and 8 kHz.

The results indicate that: 1. OHC impairment in the most basal region reduces contribution to more apically generated DPOAEs; 2. OHC impairment in a limited area, which may be revealed by DPOAEs but not by conventional audiometry, can contribute to tinnitus generation; and 3. patients with unilateral tinnitus and normal hearing on the conventional audiogram are likely to demonstrate hearing loss in the EHF region.

E-mail: k.kochanek@ifps.org.pl