Subjective Hearing Problems in Normal-Hearing Tinnitus Subjects. Background

Transcription

1 Subjective Hearing Problems in Normal-Hearing Tinnitus Subjects Background Most experts agree that the tinnitus signal is generated at least in part by discordant damage of outer hair cells (OHCs). Discordant damage refers to the phenomenon that OHCs are more susceptible to damage than their adjacent inner hair cells (IHCs). OHCs and IHCs provide input to the dorsal cochlear nucleus (DCN). Discordant damage creates imbalanced input to the DCN, resulting in abnormal high-frequency bursts of nerve activity within the DCN which then propagate throughout the auditory nervous system. These abnormal highfrequency bursts then are perceived by the auditory cortex as sound: tinnitus. OHC damage can be great enough to result in measurable hearing loss; in such cases, reduced sound input causes the auditory neural network to enhance the strength of the aberrant high-frequency signals which are finally perceived by the auditory cortex as a sound: tinnitus. However, OHC damage can be so slight that it cannot be detected by routine hearing tests and yet generate the tinnitus signal. In fact, the cochlea can sustain diffuse damage to up to 30% of the OHCs before hearing loss is measurable (Bohne & Clark,1982; Chen & Fechter, 2003). Approximately 20% of tinnitus patients have normal hearing (Davis & El Refaie, 2000). Benton (2010) reported significant differences in hearing thresholds between groups of tinnitus and non-tinnitus subjects; tinnitus subjects demonstrated better hearing than nontinnitus subjects, a finding attributed to the significant difference (p <.001) in the mean age of the two groups: the tinnitus subjects (n=644) were significantly younger (55.96 years, SD 12.45) than the non-tinnitus subjects (n = 1889, mean years, SD 13.27). Not surprisingly, hearing

2 aid use was more common among non-tinnitus subjects (58.9%) than among tinnitus subjects (41.1%). Benton s (2010) data also revealed that 45% of the tinnitus subjects had normal hearing as defined by threhsolds of 25 db HL or better at all octave frequencies Hz and at 3000 and 6000 Hz. Figure 1 presents the percentage of Tinnitus and Non-Tinnitus subjects demonstrating varying degrees of hearing loss. Figure 1. A comparison of the percentage of Tinnitus and Non-Tinnitus subjects demonstrating various degrees of hearing loss (based on four-frequency averages of 1000, 2000, 3000 and 4000 Hz). Audiologists have long been aware that tinnitus patients who demonstrated normal hearing thresholds frequently report not only substantial tinnitus-related distress but also substantial hearing and understanding difficulties that cannot be explained by their normal

3 Mean Threshold (db HL) hearing thresholds. We were interested in exploring these issues to obtain a greater understanding of normal-hearing tinnitus patients. We identified 109 normal hearing subjects who had sought tinnitus services at the VA Medical Center in Atlanta in a 6-month period. The mean hearing thresholds are shown in Figure 2 and mean acoustic reflex and speech audiometry values are shown in Table 1. The mean age of these normal-hearing tinnitus subjects was years (SD = 11.02) Right Ear Left Ear Frequency (Hz) Figure 2. Mean hearing thresholds for 109 normal-hearing tinnitus subjects

4 Right Ear Left Ear Mean 1kHz Reflex Thresholds (SD) Mean Speech Audiometry Values (SD) Contra Ipsi Contra Ipsi (7.30) (5.83) (5.49) (5.68) SRT WRS % SRT WRS % 9.63 (4.12) (6.86) 9.17 (4.52) (9.21) Table 1. Mean 1kHz reflex thresholds and speech audiometry values for 109 normal-hearing tinnitus subjects. The majority of subjects (n=93, or 82%) reported hearing their tinnitus at least 50% of waking hours, and 57 subjects (50%) reported hearing their tinnitus 100% of waking hours. Ringing was the most common tinnitus description (n=95, or 83%) and the majority of subjects experienced bilateral tinnitus (n=96, or 84%). Mental health (MH) disorders were highly prevalent among this group of normalhearing tinnitus subjects: 84 subjects (74%) had at least one diagnosed MH disorder, and 52 of these subjects (62%) had two or more diagnosed MH disorders. Table 2 presents the most commonly occurring specific MH diagnoses identified in this group of subjects. Most Commonly Occurring Mental Health Diagnoses Post-Traumatic Stress Disorder (PTSD) Only 20 (24%) Depression Only 17 (20%) PTSD + Depression 20 (24%) PTSD + Depression + Anxiety 7 (8%) Depression + Other 10 (12%) Other Diagnos(es) 10 (12%) Table 2. The most commonly occurring mental health diagnoses in a group of 84 normal-hearing tinnitus patients diagnosed with at least one mental health disorder.

5 Subjective Hearing Problems In a large study of 644 tinnitus subjects, Benton (2010) identified 199 tinnitus who had normal hearing as evidenced by binaural four-frequency averages of 25 db HL or better and who had completed the Hearing Handicap Inventory for the Elderly-Short Form, or HHIES (Weinstein, REF). Table 3 presents the mean four-frequency averages and HHIES scores for these 199 subjects, as well as the number and percentage of subjects HHIES scores falling within each hearing handicap range. Only 21% of the normal-hearing tinnitus subjects scored in the no significant hearing handicap range whereas over 1/3 (39%) scored in the severe hearing handicap range. The remainder (40%) scored in the mild-moderate hearing handicap range. More than ¾ of the subjects (79%) experienced significant hearing handicap as demonstrated by HHIES scores. N=199 Binaural 4-Freq Avg. (db HL) HHIES Score Mean SD HHIES Score Range (Handicap Category) N % Subjects 0-8 (None) 41 21% (Mild-Moderate) 80 40% 79% (Severe) 78 39% Table 3. Auditory acuity and HHIES data for 199 normal-hearing tinnitus subjects. Anecdotal reports abound regarding patients confusing s caused by tinnitus with s caused by hearing loss and vice-versa. Henry et al (REF) created the Tinnitus-

6 Hearing Survey, or THS, to help audiologists address this confusion. As shown in Table 4, this brief, simple questionnaire asks tinnitus patients to rate the size of the s caused by four specific hearing situations and four specific tinnitus situations using a 5-point scale (range of points per item = 0 4). The auditory issue with the higher total score is presumably the greater and thus is the issue requiring intervention. Although the reliability and validity of the THS have been demonstrated (Henry et al, 2015), Henry (June 24, 2015 personal communication) reported that there are no normative values for the THS as of this writing. Tinnitus My tinnitus makes it hard for me to sleep at night. My tinnitus makes it hard for me to concentrate when I'm reading. My tinnitus makes it hard for me to relax in a quiet room. It is difficult for me to focus my attention away from my tinnitus and onto other things. Hearing Loss It's hard for me to understand what others are saying in noisy or crowded places. I have a difficult time understanding what people are saying on television or in movies. It's hard for me to distinguish what's being said when children, or people with soft or high voices, talk to me. It's hard for me to participate in a group conversation because I can't understand what others are saying. No, not a small moderate big very big No, not a small moderate big very big Table 4. The Tinnitus Hearing Survey (THS).

7 We identified 26 normal-hearing tinnitus patients who had completed the THS. Scores on the THS Hearing Loss subscore were greater than those on the Tinnitus subscore for 12 subjects (46%). Table 5 presents the mean THS Hearing Loss and Tinnitus subscores for the two groups of subjects and all subjects combined, The mean Tinnitus subscore for subjects whose subscores indicated that tinnitus was the bigger was significantly higher than that of those whose subscores indicated that hearing loss was the bigger (p =.002). Cohen s d (1.31 ) indicated the difference in Tinnitus Subscores was very large. Of special importance is that the Hearing Loss subscores for both groups were not significantly different (p >.05). Furthermore, the mean Hearing Loss subscore for the group of 26 subjects was not significantly different from the mean Tinnitus subscore for all subjects (p >.05). These findings confirm that normal hearing tinnitus subjects experience substantial subjective hearing s that are not explained by their pure-tone acuity. Hearing Loss Greater (n=12) Tinnitus Greater (n=14) All Subjects (n=26) THS Tinnitus Subscore (SD)* 9.67 (4.60) (1.94) (4.10) THS Hearing Loss Subscore (SD) (4.21) (4.10) (4.13) Table 5. THS Subscores for 26 tinnitus subjects with normal hearing thresholds. (* p =.002) The Physical Health Questionnaire, or PHQ9 (REF), is a 9-item screening measure for depression. PHQ9 scores were available for all 26 subjects, as were estimates for Total Disturbance percentages, which is the percentage of waking hours that tinnitus is truly disturbing, calculated by multiplying the patient s estimate of percentage of waking hours they are aware of their tinnitus by the percentage of time they are aware of their tinnitus that it is

8 truly disturbing. There was no significant difference between the mean PHQ9 scores (p >.05) oth groups and the mean Total Disturbance values (p >.05) Mean PHQ9 scores and Total Disturbance % estimates for the two groups are presented in Table 6. Hearing Loss Greater (n=12) Tinnitus Greater (n=14) All Subjects (n=26) Total Disturbance % (SD) (29.88) (22.09) (26.20) PHQ9 Score (SD) (8.66) (5.27) (7.20) Table 6. Mean PHQ9 scores and Total Disturbance % estimates for two THS response groups. Discussion and Conclusions These findings confirm that a majority of normal hearing tinnitus subjects experience subjective hearing s. It is reasonable to assume that if, as most evidence suggests, the presence of tinnitus indicates that the cochlea has been damaged then the exquisite fine tuning of the cochlea is reduced, thus reducing its coding capabilities, especially with regards to degraded speech. Research has begun to focus on the role of the dorsal cochlear nucleus (DCN) as a critical player in the generation of the tinnitus signal. Baizer et al (2012) stated: Three major lines of evidence implicate the DCN in tinnitus. First, elevated spontaneous activity in the DCN is correlated with peripheral damage and tinnitus. Second, there are somatosensory inputs to the DCN that can modulate spontaneous activity and might mediate the somatic-auditory interactions seen in tinnitus patients [explaining why some individuals can elicit tinnitus with

9 certain movements]. Third, we have found a subpopulation of DCN neurons in the adult rat that express doublecortin, a plasticity-related protein. The expression of this protein may reflect a role of these neurons in the neural reorganization causing tinnitus. Koehler and Shore (2013) were among the first to demonstrate that alteration of DCN firing rates actually affected the presentation of tinnitus in lab animals, and experimental treatments based upon this finding are expected. In short, the research is coalescing around the theories that discordant damage/dysfunction creates aberrant nerve signals in the DCN. Because the DCN also plays a critical role in the improvement of signal-to-noise ratio (REF), abnormal DCN function may also impair this capability. Abnormal function of the auditory periphery and central auditory bodies thus may explain why normal-hearing tinnitus patients frequently report hearing complaints that are not explained by the normal hearing test, such as difficulty hearing in noise, difficulty understanding TV etc. References McCombe et al (1999). Guidelines for the grading of tinnitus severity: the results of a working group commissioned by the British Association of Otolaryngologists, Head and Neck Surgeons: Clinical Otolaryngology and Allied Sciences, Oct: 26(5): Wilson P, Henry J, Bowland M & Haralambous G. (1991). The Tinnitus Reaction Questionnaire: Psychometric properties of a measure of distress associated with tinnitus. Journal of Speech and Hearing Research, 34: