الفهرس 
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Abstract
Tinnitus is a hyperactive hearing disorder which may occur as a result of cochlear function alterations. Cochlear damage is usually manifested by increase of hearing thresholds, but the absence of hearing loss does not eliminate cochlear damage. This work aimed to diagnose the existence of hidden hearing loss (cochlear synaptopathy) in tinnitus patients with normal hearing using audiometric and electrophysiological tests. This was done by using specific, sensitive and reliable noninvasive diagnostic tests; pure tone audiometry (PTA), speech audiometry, distortion product otoacoustic emissions (DPOAEs), auditory brain stem response (ABR), electrocochleography (EchoG), threshold equalizing noise (TEN) test and tinnitus handicap inventory questionnaire (THIQ). This study included 50 subjects. They were classified into two groups. The first group was a control group which consisted of 25 adults with bilateral normal peripheral hearing. The second group was a study group which consisted of 25 adults with bilateral normal peripheral hearing complaining of tinnitus. Comparison of PTA results showed a statistically significant difference at all standard audiometric frequencies, extended high frequencies, PTA average and SRT. between the two groups. Tinnitus group showed elevated thresholds compared to the control group. However both groups had normal hearing threshold. Both groups showed 100% of word recognition score. Tinnitus Handicap Inventory Questionnaire results showed nine patients (36%) had a score of severe handicap, nine patients (36%) had a score of moderate handicap, six patients (24%) had a score of mild handicap and only one patient (4%) had a score of catastrophic handicap. Correlations between THIQ and positive significant data showed positive correlations at all PTA frequencies including extended high frequencies, PTA average, SRT, (DP 3, 4 and 7) and SNR (1, 6 and 8). There was positive correlation between both age and duration of tinnitus with tinnitus severity. According to our results, dead regions were absent in both groups with no significant threshold shift in TEN test in each group, reflecting integrity of the inner hair cells. Comparison of DPOAEs between both groups showed a statistically significant difference in DP (DP3, 4, 7) and SNR (SNR1, 3, 4, 5, 6, 8, 9) .Tinnitus patients showed decreased values compared to normal individual. Comparison of wave I amplitude in ABR between the two groups showed a statistically significant difference. Tinnitus patients had decreased amplitude compared to normal individual. Comparison of EchoG results between the two groups was done. 20% of the tinnitus patients showed SP/AP ratio more than 0.4 which strongly agreed with HHL presence. However other patients in the study group showed no statistically significant difference with the control group. AP amplitude comparison between both groups showed a statistically significant difference with decreased amplitude in tinnitus patients compared to normal individual. SP amplitude, latency and AP latency comparison between both groups showed no statistically significant difference. Correlation between age of patients, duration of tinnitus and with all other significant data showed positive correlations in all PTA frequencies including high frequencies as well as PTA average, SRT and SNR (1, 6, 7, and 8) and DP (3 and 7) with duration of tinnitus and age. There was also positive correlation between wave (I) amplitude and age. These findings denoted that PTA, DPOAEs, wave I amplitude and SP/AP ratio results are sensitive indicators for the presence of HHL. These results support the hypothesis of HHL presence in tinnitus patients.