Otology & Neurotology 35:1026Y1032 Ó 2014, Otology & Neurotology, Inc.
Willingness-to-Accept Gamma Knife Radiosurgery for Tinnitus Among Career San Francisco Firefighters *Seth E. Pross, *Camille A. Allen, †Oi Saeng Hong, and *Steven W. Cheung *Department of OtolaryngologyYHead and Neck Surgery, and ÞDepartment of Community Health Systems, University of California, San Francisco, California, U.S.A.
Objective: Measure willingness-to-accept novel Gamma knife (GK) radiosurgery of the caudate nucleus to treat tinnitus among career firefighters who are at higher risk of hearing loss because of occupational noise exposure. Study Design: Cross-sectional survey. Materials and Methods: A Web-based 80-item survey was distributed to 800 San Francisco firefighters and satisfactorily completed by 101 respondents. Demographic and work-related characteristics including occupational noise exposure, hearing handicap using the Hearing Handicap Inventory for Adults (HHIA), and tinnitus severity using the tinnitus functional index (TFI) were assessed. Willingness-to-accept GK radiosurgery for tinnitus was profiled using a 7-point scale for 6 decremental levels of expected tinnitus improvement. Results: Respondents were a majority male (82%) and Caucasian (56%). Nearly all (95%) reported significant daily or weekly
occupational noise exposure. Mean HHIA (16.3) and mean TFI (14.6) were mild. At the 100% (complete) tinnitus improvement level, more than 60% of respondents were ‘‘likely’’ willingto-accept Gamma knife radiosurgery. At the 75% tinnitus improvement level, 43% of respondents were ‘‘likely’’ willingto-accept GK radiosurgery. Below the 75% tinnitus improvement level, willingness-to-accept dropped off steeply. Conclusion: Gamma knife radiosurgery to area LC, a locus of the caudate nucleus, for tinnitus would be of interest to a large population with moderate or lower tinnitus distress. Should this innovative intervention be considered in the future, a rigorous clinical trial will be necessary to establish safety and efficacy. Key Words: FirefightersVGamma knifeVHearing Handicap Inventory for AdultsVOccupational noise exposureVTinnitusV Tinnitus functional index. Otol Neurotol 35:1026Y1032, 2014.
Subjective tinnitus is defined as auditory percepts without a physical correlate. Chronic subjective tinnitus affects 10% to 15% of the population with a peak incidence up to 27% in the seventh and eighth decades of life (1,2). Although 80% of patients with chronic tinnitus adapt well to their auditory phantom, a sizeable minority are troubled enough to seek medical attention because of degradation of their quality of life (1). On a cross-sectional basis, the level of tinnitus distress cannot be predicted by auditory phantom loudness, pitch, or maskability (3). Societal health-care costs associated with chronic tinnitus are significant. For example, tinnitus is the most common service connected disability claim in the U.S. Department of Veterans Affairs. Compensation payout was $1.1 billion in 2011 and projected to be $2.3 billion by 2014 (4).
Although many causes of tinnitus are known, including cerebrovascular disease, autoimmune disorders, inner ear disorders, and high-dose aspirin, acoustic trauma is thought to be the most common (1,5). Once tinnitus becomes chronic, peripheral auditory deafferentation by cochlear nerve section does not reliably eliminate the auditory phantom (6). This finding supports an important role for central nervous system engagement in persistent tinnitus. The close association between hearing loss and tinnitus has created a considerable challenge to isolate central auditory changes that can be clearly attributable to auditory phantoms (7). Nonetheless, the dominant treatment approach has been directed at targeting the auditory system, primarily through hearing aids and maskers, in addition to behavioral modification and adaptation strategies. Recently, a nonauditory basal ganglia-based treatment approach to suppress tinnitus was introduced, motivated by acute experiments and clinical observations in humans. Experimental studies of temporary focal neuromodulation in area LC, a site of the caudate positioned at the junction of the head and body of the nucleus, using a commercial deep brain stimulation (DBS) lead in movement disorders patients showed reproducible and reversible
Address correspondence and reprint requests to Steven W. Cheung, M.D., Department of OtolaryngologyYHead and Neck Surgery, 2233 Post St, 3rd Floor, San Francisco, CA 94115; E-mail: [email protected] Sources of Support: Departmental Funds. The authors disclose no conflicts of interest.
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TINNITUS AMONG FIREFIGHTERS tinnitus modulation effects typically on the order of minutes to days. Although auditory phantom loudness and sound quality were modulated, audiometric configurations remained unchanged (5,8). The most promising short-term tinnitus suppression results came from high-frequency stimulation, which is generally believed to inactivate local neural elements. There is not yet long-term tinnitus suppression data in patients chronically stimulated with a DBS lead permanently positioned in area LC. As such, it should be recognized that area LC neuromodulation by DBS is invasive and unproven, but this experimental intervention may be acceptable to certain suitably distressed tinnitus patients. An alternative experimental approach is to inactivate area LC irreversibly by lesioning the treatment target using a noninvasive modality. Support for this innovative methodology is derived from 2 case reports of basal ganglia infarctions that involve area LC. In those 2 stroke patients, substantial tinnitus suppression lasted for at least 18 months (9,10). A candidate therapeutic tool to inactivate area LC focally, analogous to infarction, is Gamma knife radiosurgery. This stereotactic external technique uses 201 sources of cobalt-60 radiation to treat intracranial pathology, including brain tumors, arteriovenous malformations, and functional targets. Stereotactic radiosurgery (SRS) has been used in functional neurosurgery to treat patients who are candidates for thalotomy, pallidotomy, and subthalotomy. In contrast to DBS, SRS is not an open procedure and carries no risk of intracranial hemorrhage or postoperative infection. On the other hand, SRS may have more uncertainty in target identification as there is no intraoperative confirmation (11). Whereas Duma et al. showed that functional SRS was effective and safe with no neurologic complication in 34 patients at 1 center (12), others have reported occasional serious complications such as visual field defects, new movement disorders, hemiparesis, and even death due to dysphagia and aspiration (13,14). Complications are thought to be results of unexpectedly larger lesions that impair neighboring structures (11). Overall, complications are rare. Because of the relatively low-risk profile associated with Gamma knife radiosurgery, it represents an essentially noninvasive alternative to DBS for focal inactivation of the area LC to treat chronic tinnitus. A population at risk for chronic tinnitus is firefighters, who are exposed to significant noise from a variety of sources, including vehicles, sirens, alarms, and trade tools (15). Occupational noise exposure would seem to place firefighters at an increased risk for both hearing loss and tinnitus. Interestingly, the English literature on firefighter hearing health is mixed with regard to whether firefighters have an increased risk of hearing loss compared with controls (16Y22). There are no studies that specifically examine tinnitus among firefighters in Medline. The goals of this pilot study were to characterize hearing handicap and tinnitus severity in the study cohort and to perform a tradeoff analysis of the willingness-to-accept Gamma knife radiosurgery for tinnitus mitigation against expected level of tinnitus improvement. Information derived
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from the latter would be important to estimate sample size for a Phase I clinical trial. MATERIALS AND METHODS Study Design A cross-sectional descriptive design was used. An online Web-based 80-item survey was approved by the Committee on Human Research at our tertiary care institution and distributed to career firefighters in the San Francisco Fire Department (SFFD) via e-mail using a union list-serve of approximately 800 addresses. All information captured was deidentified. The survey recorded demographic characteristics as well as information on work and home noise exposure levels. Hearing handicap was assessed using the Hearing Handicap Inventory for Adults (HHIA), a 25-item self-reported instrument (23). The HHIA has been demonstrated to have an excellent test-retest reliability (r = 0.97), low standard error of measurement (4.2), and high internal consistency reliability (Cronbach’s alpha = 0.93) (23, 24). Tinnitus severity was assessed using the tinnitus functional index (TFI), also a 25-item self-reported instrument. The TFI has been shown to have good test-retest reliability (r = 0.78) and excellent internal consistency reliability (Cronbach’s alpha = 0.97) (25). Willingness-to-accept Gamma knife radiosurgery for tinnitus was profiled using a 7-point scale (1 = never, 2 = very unlikely, 3 = unlikely, 4 = neutral, 5 = likely, 6 = very likely, and 7 = definitely) for a series of expected tinnitus improvement levels that spanned from ‘‘complete (100%)’’ to ‘‘a bit (10%).’’ Data were exported to the Microsoft Excel spreadsheet computing environment. Statistical analyses were performed using the Data Analysis toolkit. Among the 800 firefighters who were invited to the study, a total of 149 started the survey (19% response rate). Of the 149 initial respondents, 110 completed the survey (74% completion rate). Of the 110 completed surveys, 9 were excluded because of irrational responses. Irrational responses were defined as increased willingness-to-accept Gamma knife radiosurgery in the setting of decreased tinnitus improvement expectation. Survey respondents were financially compensated with a $15 gift-card to Starbucks for their time and participation. A flow diagram of respondent accrual is shown in Figure 1. Data analysis was focused on rational respondents (n = 101).
RESULTS Demographic and Occupational Characteristics Demographic characteristics of the rational respondents are representative of all respondents (Table 1). The population was predominantly male (82%). The mean age of respondents was 46.8 years, with a range of 28 to 63 years. Race/ethnicity distribution was Caucasian (56%), Hispanic or Latino (22%), and Asian or Pacific Islander (22%). The mean years working as a firefighter was 17.6, with a range of 0 to 36 years. Occupational demographic features are presented in Table 2. Nearly all respondents reported significant loud noise exposure at work either daily (61%) or weekly (34%). Only a minority reported loud noise exposure at home daily (3%) or weekly (23%). Lifetime noise exposure was reported at a mean of 4.3 on a 7-point scale (1 = minor, 4 = major, and 7 = extreme). The percentage of total time using hearing protection on the last emergency (or fire) run was 64% Otology & Neurotology, Vol. 35, No. 6, 2014
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S. E. PROSS ET AL. ‘‘significant handicap (943)’’ (Fig. 2). Roughly one-third of firefighters rated themselves as having some level of hearing handicap. Tinnitus Severity Tinnitus severity as assessed by TFI showed a mean of 14.6 and a median of 10.8, also indicating a skewed distribution (Table 1). Frequency distribution by tinnitus severity showed that for 48% tinnitus was ‘‘not a problem (0Y9),’’ 24% had a ‘‘small problem (10Y20),’’ 13% had a ‘‘small-to-moderate problem (21Y29),’’ and 15% had a ‘‘moderate problem or greater (Q30)’’ (Fig. 3). Overall, 85% of firefighters had a moderate or lesser problem with tinnitus. A linear regression analysis was performed to evaluate the relationship between HHIA and TFI, which showed no statistically significant relationship, likely because of relatively small sample size and narrow range of TFI values (data not shown).
FIG. 1.
Respondent accrual flow diagram.
and over the past 3 months of run times was 49%, with wide ranges (0%Y100%) for both. Hearing Handicap Hearing handicap as assessed by HHIA showed a mean of 16.3 and median of 10.0, indicating a skewed distribution (Table 1). Frequency distribution by hearing handicap severity revealed 64% had ‘‘no handicap (0Y16),’’ 27% had ‘‘mild-to-moderate handicap (17Y42),’’ and 9% had TABLE 1. Demographic characteristics Sex Male Female Other/no response Age (yr) Mean (SD) Median Range Race/ethnicity African American or Black American Indian or Alaska Native Asian or Pacific Islander Hispanic or Latino Caucasian Other race or ethnicity Years as firefighter Mean (SD) Median Range Hearing handicap in adults (HHIA) Mean (SD) Median Range Tinnitus functional index (TFI) Mean (SD) Median Range
Willingness-to-Accept Gamma Knife Radiosurgery Respondents were given information about Gamma knife radiosurgery for tinnitus (Figure 4) and asked to rate their likelihood of accepting Gamma knife radiosurgery to the area LC for tinnitus on a 7-point scale (1 = never, 2 = very unlikely, 3 = unlikely, 4 = neutral, 5 = likely, 6 = very likely, and 7 = definitely) across decreasing levels of expected tinnitus improvement (100% [complete], 90%, 75%, 50%, 25%, and 10% [a bit]). The willingness-toaccept Gamma knife radiosurgery for tinnitus profile of respondents who were at least ‘‘likely’’ (i.e., marked 5, 6, or 7 on the 7-point rating scale) is displayed in Figure 5.
Basic demographic characteristics All respondents (N = 149)
Rational respondents (n = 101)
121 (81%) 26 (17%) (1%)
83 (82%) 18 (18%) (0%)
46.6 (8.1) 47.0 28Y68 6% 1% 25% 17% 53% 1%
46.8 (7.8) 47.0 28Y63 7% 1% 22% 22% 56% 1%
17.0 (7.8) 18.0 0Y36
17.6 (7.8) 18.0 0Y36
17.2 (18.4) 11.0 0Y98
16.0 (16.3) 10.0 0Y66
15.2 (16.3) 11.4 0Y65.6
14.6 (15.9) 10.8 0Y65.6
Otology & Neurotology, Vol. 35, No. 6, 2014
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TINNITUS AMONG FIREFIGHTERS TABLE 2.
Occupational demographic features
Occupational features
All respondents (N = 149)
Work noise exposure Rarely Uncommonly Monthly Weekly Daily Home noise exposure Rarely Uncommonly Monthly Weekly Daily Lifetime noise exposure (1 = minor, 4 = major, 7 = extreme) Mean (SD) Median Range Hearing protection last run (% of total run time) Mean (SD) Median Range Hearing protection last 3 months (% of total run times) Mean (SD) Median Range
There was monotonic decline in the proportion of respondents who would accept SRS with decreasing expected benefit. At the 100% (complete) tinnitus improvement level, ‘‘likely,’’ ‘‘very likely,’’ or ‘‘definitely’’ willingnessto-accept Gamma knife radiosurgery was 62%. At the 75% tinnitus improvement level, willingness-to-accept was 43%. Below the 75% level, willingness-to-accept GK dropped off steeply. Regression analyses were performed to evaluate the relationship between willingness-to-accept Gamma knife radiosurgery for treatment of tinnitus and covariates including the number of years serving as a firefighter, age, home noise exposure, lifetime noise exposure, use of hearing protection during the last emergency run, and use
FIG. 2.
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Rational respondents (n = 101)
2 (1%) 1 (1%) 3 (2%) 54 (36%) 80 (54%)
2 1 2 34 62
(2%) (1%) (2%) (34%) (61%)
46 (31%) 39 (26%) 26 (17%) 26 (17%) 3 (2%)
32 29 14 23 3
(32%) (29%) (14%) (23%) (3%)
4.4 (1.4) 4.0 1Y7
4.3 (1.3) 4.0 2Y7
62% (41%) 80% 0%Y100%
64% (40%) 80% 0%Y100%
46% (37%) 50% 0%Y100%
49% (36%) 50% 0%Y100%
of hearing protection over the last 3 months. Regression analyses were also performed to evaluate the relationship between TFI and HHIA scores with the willingness-toaccept Gamma knife radiosurgery. Additionally, regression analyses were performed to evaluate the relationship between TFI and age, years as firefighter, and workrelated noise exposure. All correlations were weak and not statistically significant (p 9 0.05, data not shown).
DISCUSSION Tinnitus suppression resulting from long-term focal inactivation by infarction (9,10) and short-term inactivation
Hearing handicap by HHIA. Otology & Neurotology, Vol. 35, No. 6, 2014
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FIG. 3.
S. E. PROSS ET AL.
Tinnitus severity by TFI.
by neuromodulation of area LC (5,8) raise consideration for development of a noninvasive treatment tool to accomplish what invasive DBS has to offer: severity reduction that does not require active patient participation to manage acoustic devices or devotion of cognitive resources to behavioral therapies. Within this framework of nonauditory basal ganglia-based neuromodulation therapy for tinnitus, it should be recognized that DBS is reversible and titratable to optimize benefit, but SRS is both irreversible and nontitratable. Those 2 important disadvantages of SRS
FIG. 4.
compared with DBS may, however, be offset by the former treatment technique’s noninvasive approach. The principal goals of this pilot study were to perform a tradeoff analysis of willingness-to-accept novel therapy versus expected level of tinnitus improvement and to characterize tinnitus severity in the study cohort. Firefighters were chosen for this study as they experience significant intermittent noise exposure, which may put them at a higher risk for chronic tinnitus. They also represent a generally healthy cohort that could be extrapolated to the
Information about Gamma knife radiosurgery for tinnitus.
Otology & Neurotology, Vol. 35, No. 6, 2014
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TINNITUS AMONG FIREFIGHTERS
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Gamma knife radiosurgery to area LC of the caudate would be of interest to a large population of patients with moderate or lower tinnitus distress. Surveying San Francisco firefighters, this willingness-to-accept novel treatment study estimates that more than 40% would be at least ‘‘likely’’ to accept Gamma knife radiosurgery if 75% tinnitus improvement could be delivered. Should this innovative intervention be considered in the future, a rigorous clinical trial will be necessary to establish safety and efficacy. Acknowledgments: The authors thank Joanne Hayes-White, chief of the San Francisco Fire Department; Thomas O’Connor, president of San Francisco Firefighters Local 798; and all of the respondents for their collaboration and assistance. FIG. 5. Willingness-to-accept Gamma knife radiosurgery for tinnitus across decreasing levels of expected tinnitus improvement.
REFERENCES
wider population of tinnitus patients. This study found 64% of the respondents had no hearing handicap and 85% had a moderate or lesser problem with tinnitus. Self-reported work-related noise exposure and tinnitus distress level was uncorrelated. Remarkably, at the 75% level of expected tinnitus improvement, more than 40% would be ‘‘likely,’’ ‘‘very likely,’’ or ‘‘definitely’’ willing-to-accept Gamma knife radiosurgery. This indicates strong interest among tinnitus patients with relatively mild severity to consider a novel noninvasive therapy to suppress their auditory phantoms. In the subpopulation of more highly distressed tinnitus patients who seek treatment by an otologist or a hearing professional at a tinnitus clinic, they may be as willing, or possibly more willing, to accept Gamma knife radiosurgery. This hypothesis can be tested in a future study. As a pilot study with a relatively small sample size using an opportunity sampling procedure, the results are subject to a number of limitations. First, this anonymous survey has a relatively low response rate of 18.6% and is susceptible to respondent bias. Extrapolation of prevalence data to the general population of firefighters may not be appropriate. Second, firefighters may be distinct from the general population. By the nature of their dangerous work, they may represent a group that is less risk averse and more willing-to-accept novel treatments than the general population. Third, the representation of potential Gamma knife radiosurgery treatment risks may be inadequate, thereby potentially impacting risk to benefit tradeoff attitudes among respondents. Fourth, virtually all anonymous survey instruments do not control for respondent mood and motivationVfactors that can also impact response data. Fifth, the sampling was geographically limited to an urban fire department in California. For a more comprehensive description of willingness-toaccept profile of Gamma knife radiosurgery for tinnitus, nationwide sampling would be necessary to capture data that span the entire spectrum of tinnitus distress severity. More highly distressed tinnitus patients may be more willing to accept SRS for tinnitus.
1. Henry JA, Dennis KC, Schechter MA. General review of tinnitus: prevalence, mechanisms, effects, and management. J Speech Lang Hear Res 2005;48:1204Y35. 2. Kochkin S, Tyler R, Born J. MarkeTrak VIII: the prevalence of tinnitus in the united states and the self-reported efficacy of various treatments. Hear Rev 2011;18:10Y26. 3. Jastreboff PJ. Tinnitus retraining therapy. In: Progress in Brain Research. Elsevier, 415Y23. 4. Congressional Hearing before a Joint Session of the House and Senate Committees on Veterans’ Affairs, 2nd Session, 112th Congress Sess. March 22, 2012). 5. Larson PS, Cheung SW. Deep brain stimulation in area LC controllably triggers auditory phantom percepts. Neurosurgery 2012;70:398Y405; discussion 405Y406. 6. Pulec JL. Cochlear nerve section for intractable tinnitus. Ear Nose Throat J 1995;74:468, 470Y476. 7. Norena AJ, Moffat G, Blanc JL, Pezard L, Cazals Y. Neural changes in the auditory cortex of awake guinea pigs after two tinnitus inducers: salicylate and acoustic trauma. Neuroscience 2010;166:1194Y209. 8. Cheung SW, Larson PS. Tinnitus modulation by deep brain stimulation in locus of caudate neurons (area LC). Neuroscience 2010;169: 1768Y78. 9. Lowry LD, Eisenman LM, Saunders JC. An absence of tinnitus. Otol Neurotol 2004;25:474Y8. 10. Larson PS, Cheung SW. A stroke of silence: tinnitus suppression following placement of a deep brain stimulation electrode with infarction in area LC. J Neurosurg 2013;118:192Y4. 11. Frighetto L, Bizzi J, Annes RD, Silva Rdos S, Oppitz P. Stereotactic radiosurgery for movement disorders. Surg Neurol Int 2012;3: S10Y6. 12. Duma CM, Jacques DB, Kopyov OV, Mark RJ, Copcutt B, Farokhi HK. Gamma knife radiosurgery for thalamotomy in parkinsonian tremor: a five-year experience. J Neurosurg 1998;88:1044Y9. 13. Okun MS, Stover NP, Subramanian T, et al. Complications of gamma knife surgery for parkinson disease. Arch Neurol 2001;58:1995Y2002. 14. Siderowf A, Gollump SM, Stern MB, Baltuch GH, Riina HA. Emergence of complex, involuntary movements after gamma knife radiosurgery for essential tremor. Mov Disord 2001;16:965Y7. 15. Hong O, Samo D, Hulea R, Eakin B. Perception and attitudes of firefighters on noise exposure and hearing loss. J Occup Environ Hyg 2008;5:210Y5. 16. Clark WW, Bohl CD. Hearing levels of firefighters: risk of occupational noise-induced hearing loss assessed by cross-sectional and longitudinal data. Ear Hear 2005;26:327Y40. 17. Pepe PE, Jerger J, Miller RH, Jerger S. Accelerated hearing loss in urban emergency medical services firefighters. Ann Emerg Med 1985;14:438Y42. Otology & Neurotology, Vol. 35, No. 6, 2014
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18. Rubak T, Kock S, Koefoed-Nielsen B, Lund SP, Bonde JP, Kolstad HA. The risk of tinnitus following occupational noise exposure in workers with hearing loss or normal hearing. Int J Audiol 2008;47:109Y14. 19. Kales SN, Freyman RL, Hill JM, Polyhronopoulos GN, Aldrich JM, Christiani DC. Firefighters’ hearing: a comparison with population databases from the international standards organization. J Occup Environ Med 2001;43:650Y6. 20. Hong O, Chin DL, Samo DG. Hearing loss and use of hearing protection among career firefighters in the united states. J Occup Environ Med 2013;55:960Y5. 21. Ide CW. Hearing losses in whole time firefighters occurring early in their careers. Occup Med (Lond) 2011;61:509Y11.
22. Chung IS, Chu IM, Cullen MR. Hearing effects from intermittent and continuous noise exposure in a study of Korean factory workers and firefighters. BMC Public Health 2012;12:87,2458-12-87. 23. Newman CW, Weinstein BE, Jacobson GP, Hug GA. The hearing handicap inventory for adults: psychometric adequacy and audiometric correlates. Ear Hear 1990;11:430Y3. 24. Newman CW, Weinstein BE, Jacobson GP, Hug GA. Test-retest reliability of the hearing handicap inventory for adults. Ear Hear 1991;12:355Y7. 25. Meikle MB, Henry JA, Griest SE, et al. The tinnitus functional index: development of a new clinical measure for chronic, intrusive tinnitus. Ear Hear 2012;33:153Y76.
Otology & Neurotology, Vol. 35, No. 6, 2014
Copyright © 2014 Otology & Neurotology, Inc. Unauthorized reproduction of this article is prohibited.
Willingness-to-Accept Gamma Knife Radiosurgery for Tinnitus Among Career San Francisco Firefighters *Seth E. Pross, *Camille A. Allen, †Oi Saeng Hong, and *Steven W. Cheung *Department of OtolaryngologyYHead and Neck Surgery, and ÞDepartment of Community Health Systems, University of California, San Francisco, California, U.S.A.
Objective: Measure willingness-to-accept novel Gamma knife (GK) radiosurgery of the caudate nucleus to treat tinnitus among career firefighters who are at higher risk of hearing loss because of occupational noise exposure. Study Design: Cross-sectional survey. Materials and Methods: A Web-based 80-item survey was distributed to 800 San Francisco firefighters and satisfactorily completed by 101 respondents. Demographic and work-related characteristics including occupational noise exposure, hearing handicap using the Hearing Handicap Inventory for Adults (HHIA), and tinnitus severity using the tinnitus functional index (TFI) were assessed. Willingness-to-accept GK radiosurgery for tinnitus was profiled using a 7-point scale for 6 decremental levels of expected tinnitus improvement. Results: Respondents were a majority male (82%) and Caucasian (56%). Nearly all (95%) reported significant daily or weekly
occupational noise exposure. Mean HHIA (16.3) and mean TFI (14.6) were mild. At the 100% (complete) tinnitus improvement level, more than 60% of respondents were ‘‘likely’’ willingto-accept Gamma knife radiosurgery. At the 75% tinnitus improvement level, 43% of respondents were ‘‘likely’’ willingto-accept GK radiosurgery. Below the 75% tinnitus improvement level, willingness-to-accept dropped off steeply. Conclusion: Gamma knife radiosurgery to area LC, a locus of the caudate nucleus, for tinnitus would be of interest to a large population with moderate or lower tinnitus distress. Should this innovative intervention be considered in the future, a rigorous clinical trial will be necessary to establish safety and efficacy. Key Words: FirefightersVGamma knifeVHearing Handicap Inventory for AdultsVOccupational noise exposureVTinnitusV Tinnitus functional index. Otol Neurotol 35:1026Y1032, 2014.
Subjective tinnitus is defined as auditory percepts without a physical correlate. Chronic subjective tinnitus affects 10% to 15% of the population with a peak incidence up to 27% in the seventh and eighth decades of life (1,2). Although 80% of patients with chronic tinnitus adapt well to their auditory phantom, a sizeable minority are troubled enough to seek medical attention because of degradation of their quality of life (1). On a cross-sectional basis, the level of tinnitus distress cannot be predicted by auditory phantom loudness, pitch, or maskability (3). Societal health-care costs associated with chronic tinnitus are significant. For example, tinnitus is the most common service connected disability claim in the U.S. Department of Veterans Affairs. Compensation payout was $1.1 billion in 2011 and projected to be $2.3 billion by 2014 (4).
Although many causes of tinnitus are known, including cerebrovascular disease, autoimmune disorders, inner ear disorders, and high-dose aspirin, acoustic trauma is thought to be the most common (1,5). Once tinnitus becomes chronic, peripheral auditory deafferentation by cochlear nerve section does not reliably eliminate the auditory phantom (6). This finding supports an important role for central nervous system engagement in persistent tinnitus. The close association between hearing loss and tinnitus has created a considerable challenge to isolate central auditory changes that can be clearly attributable to auditory phantoms (7). Nonetheless, the dominant treatment approach has been directed at targeting the auditory system, primarily through hearing aids and maskers, in addition to behavioral modification and adaptation strategies. Recently, a nonauditory basal ganglia-based treatment approach to suppress tinnitus was introduced, motivated by acute experiments and clinical observations in humans. Experimental studies of temporary focal neuromodulation in area LC, a site of the caudate positioned at the junction of the head and body of the nucleus, using a commercial deep brain stimulation (DBS) lead in movement disorders patients showed reproducible and reversible
Address correspondence and reprint requests to Steven W. Cheung, M.D., Department of OtolaryngologyYHead and Neck Surgery, 2233 Post St, 3rd Floor, San Francisco, CA 94115; E-mail: [email protected] Sources of Support: Departmental Funds. The authors disclose no conflicts of interest.
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Copyright © 2014 Otology & Neurotology, Inc. Unauthorized reproduction of this article is prohibited.
TINNITUS AMONG FIREFIGHTERS tinnitus modulation effects typically on the order of minutes to days. Although auditory phantom loudness and sound quality were modulated, audiometric configurations remained unchanged (5,8). The most promising short-term tinnitus suppression results came from high-frequency stimulation, which is generally believed to inactivate local neural elements. There is not yet long-term tinnitus suppression data in patients chronically stimulated with a DBS lead permanently positioned in area LC. As such, it should be recognized that area LC neuromodulation by DBS is invasive and unproven, but this experimental intervention may be acceptable to certain suitably distressed tinnitus patients. An alternative experimental approach is to inactivate area LC irreversibly by lesioning the treatment target using a noninvasive modality. Support for this innovative methodology is derived from 2 case reports of basal ganglia infarctions that involve area LC. In those 2 stroke patients, substantial tinnitus suppression lasted for at least 18 months (9,10). A candidate therapeutic tool to inactivate area LC focally, analogous to infarction, is Gamma knife radiosurgery. This stereotactic external technique uses 201 sources of cobalt-60 radiation to treat intracranial pathology, including brain tumors, arteriovenous malformations, and functional targets. Stereotactic radiosurgery (SRS) has been used in functional neurosurgery to treat patients who are candidates for thalotomy, pallidotomy, and subthalotomy. In contrast to DBS, SRS is not an open procedure and carries no risk of intracranial hemorrhage or postoperative infection. On the other hand, SRS may have more uncertainty in target identification as there is no intraoperative confirmation (11). Whereas Duma et al. showed that functional SRS was effective and safe with no neurologic complication in 34 patients at 1 center (12), others have reported occasional serious complications such as visual field defects, new movement disorders, hemiparesis, and even death due to dysphagia and aspiration (13,14). Complications are thought to be results of unexpectedly larger lesions that impair neighboring structures (11). Overall, complications are rare. Because of the relatively low-risk profile associated with Gamma knife radiosurgery, it represents an essentially noninvasive alternative to DBS for focal inactivation of the area LC to treat chronic tinnitus. A population at risk for chronic tinnitus is firefighters, who are exposed to significant noise from a variety of sources, including vehicles, sirens, alarms, and trade tools (15). Occupational noise exposure would seem to place firefighters at an increased risk for both hearing loss and tinnitus. Interestingly, the English literature on firefighter hearing health is mixed with regard to whether firefighters have an increased risk of hearing loss compared with controls (16Y22). There are no studies that specifically examine tinnitus among firefighters in Medline. The goals of this pilot study were to characterize hearing handicap and tinnitus severity in the study cohort and to perform a tradeoff analysis of the willingness-to-accept Gamma knife radiosurgery for tinnitus mitigation against expected level of tinnitus improvement. Information derived
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from the latter would be important to estimate sample size for a Phase I clinical trial. MATERIALS AND METHODS Study Design A cross-sectional descriptive design was used. An online Web-based 80-item survey was approved by the Committee on Human Research at our tertiary care institution and distributed to career firefighters in the San Francisco Fire Department (SFFD) via e-mail using a union list-serve of approximately 800 addresses. All information captured was deidentified. The survey recorded demographic characteristics as well as information on work and home noise exposure levels. Hearing handicap was assessed using the Hearing Handicap Inventory for Adults (HHIA), a 25-item self-reported instrument (23). The HHIA has been demonstrated to have an excellent test-retest reliability (r = 0.97), low standard error of measurement (4.2), and high internal consistency reliability (Cronbach’s alpha = 0.93) (23, 24). Tinnitus severity was assessed using the tinnitus functional index (TFI), also a 25-item self-reported instrument. The TFI has been shown to have good test-retest reliability (r = 0.78) and excellent internal consistency reliability (Cronbach’s alpha = 0.97) (25). Willingness-to-accept Gamma knife radiosurgery for tinnitus was profiled using a 7-point scale (1 = never, 2 = very unlikely, 3 = unlikely, 4 = neutral, 5 = likely, 6 = very likely, and 7 = definitely) for a series of expected tinnitus improvement levels that spanned from ‘‘complete (100%)’’ to ‘‘a bit (10%).’’ Data were exported to the Microsoft Excel spreadsheet computing environment. Statistical analyses were performed using the Data Analysis toolkit. Among the 800 firefighters who were invited to the study, a total of 149 started the survey (19% response rate). Of the 149 initial respondents, 110 completed the survey (74% completion rate). Of the 110 completed surveys, 9 were excluded because of irrational responses. Irrational responses were defined as increased willingness-to-accept Gamma knife radiosurgery in the setting of decreased tinnitus improvement expectation. Survey respondents were financially compensated with a $15 gift-card to Starbucks for their time and participation. A flow diagram of respondent accrual is shown in Figure 1. Data analysis was focused on rational respondents (n = 101).
RESULTS Demographic and Occupational Characteristics Demographic characteristics of the rational respondents are representative of all respondents (Table 1). The population was predominantly male (82%). The mean age of respondents was 46.8 years, with a range of 28 to 63 years. Race/ethnicity distribution was Caucasian (56%), Hispanic or Latino (22%), and Asian or Pacific Islander (22%). The mean years working as a firefighter was 17.6, with a range of 0 to 36 years. Occupational demographic features are presented in Table 2. Nearly all respondents reported significant loud noise exposure at work either daily (61%) or weekly (34%). Only a minority reported loud noise exposure at home daily (3%) or weekly (23%). Lifetime noise exposure was reported at a mean of 4.3 on a 7-point scale (1 = minor, 4 = major, and 7 = extreme). The percentage of total time using hearing protection on the last emergency (or fire) run was 64% Otology & Neurotology, Vol. 35, No. 6, 2014
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S. E. PROSS ET AL. ‘‘significant handicap (943)’’ (Fig. 2). Roughly one-third of firefighters rated themselves as having some level of hearing handicap. Tinnitus Severity Tinnitus severity as assessed by TFI showed a mean of 14.6 and a median of 10.8, also indicating a skewed distribution (Table 1). Frequency distribution by tinnitus severity showed that for 48% tinnitus was ‘‘not a problem (0Y9),’’ 24% had a ‘‘small problem (10Y20),’’ 13% had a ‘‘small-to-moderate problem (21Y29),’’ and 15% had a ‘‘moderate problem or greater (Q30)’’ (Fig. 3). Overall, 85% of firefighters had a moderate or lesser problem with tinnitus. A linear regression analysis was performed to evaluate the relationship between HHIA and TFI, which showed no statistically significant relationship, likely because of relatively small sample size and narrow range of TFI values (data not shown).
FIG. 1.
Respondent accrual flow diagram.
and over the past 3 months of run times was 49%, with wide ranges (0%Y100%) for both. Hearing Handicap Hearing handicap as assessed by HHIA showed a mean of 16.3 and median of 10.0, indicating a skewed distribution (Table 1). Frequency distribution by hearing handicap severity revealed 64% had ‘‘no handicap (0Y16),’’ 27% had ‘‘mild-to-moderate handicap (17Y42),’’ and 9% had TABLE 1. Demographic characteristics Sex Male Female Other/no response Age (yr) Mean (SD) Median Range Race/ethnicity African American or Black American Indian or Alaska Native Asian or Pacific Islander Hispanic or Latino Caucasian Other race or ethnicity Years as firefighter Mean (SD) Median Range Hearing handicap in adults (HHIA) Mean (SD) Median Range Tinnitus functional index (TFI) Mean (SD) Median Range
Willingness-to-Accept Gamma Knife Radiosurgery Respondents were given information about Gamma knife radiosurgery for tinnitus (Figure 4) and asked to rate their likelihood of accepting Gamma knife radiosurgery to the area LC for tinnitus on a 7-point scale (1 = never, 2 = very unlikely, 3 = unlikely, 4 = neutral, 5 = likely, 6 = very likely, and 7 = definitely) across decreasing levels of expected tinnitus improvement (100% [complete], 90%, 75%, 50%, 25%, and 10% [a bit]). The willingness-toaccept Gamma knife radiosurgery for tinnitus profile of respondents who were at least ‘‘likely’’ (i.e., marked 5, 6, or 7 on the 7-point rating scale) is displayed in Figure 5.
Basic demographic characteristics All respondents (N = 149)
Rational respondents (n = 101)
121 (81%) 26 (17%) (1%)
83 (82%) 18 (18%) (0%)
46.6 (8.1) 47.0 28Y68 6% 1% 25% 17% 53% 1%
46.8 (7.8) 47.0 28Y63 7% 1% 22% 22% 56% 1%
17.0 (7.8) 18.0 0Y36
17.6 (7.8) 18.0 0Y36
17.2 (18.4) 11.0 0Y98
16.0 (16.3) 10.0 0Y66
15.2 (16.3) 11.4 0Y65.6
14.6 (15.9) 10.8 0Y65.6
Otology & Neurotology, Vol. 35, No. 6, 2014
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TINNITUS AMONG FIREFIGHTERS TABLE 2.
Occupational demographic features
Occupational features
All respondents (N = 149)
Work noise exposure Rarely Uncommonly Monthly Weekly Daily Home noise exposure Rarely Uncommonly Monthly Weekly Daily Lifetime noise exposure (1 = minor, 4 = major, 7 = extreme) Mean (SD) Median Range Hearing protection last run (% of total run time) Mean (SD) Median Range Hearing protection last 3 months (% of total run times) Mean (SD) Median Range
There was monotonic decline in the proportion of respondents who would accept SRS with decreasing expected benefit. At the 100% (complete) tinnitus improvement level, ‘‘likely,’’ ‘‘very likely,’’ or ‘‘definitely’’ willingnessto-accept Gamma knife radiosurgery was 62%. At the 75% tinnitus improvement level, willingness-to-accept was 43%. Below the 75% level, willingness-to-accept GK dropped off steeply. Regression analyses were performed to evaluate the relationship between willingness-to-accept Gamma knife radiosurgery for treatment of tinnitus and covariates including the number of years serving as a firefighter, age, home noise exposure, lifetime noise exposure, use of hearing protection during the last emergency run, and use
FIG. 2.
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Rational respondents (n = 101)
2 (1%) 1 (1%) 3 (2%) 54 (36%) 80 (54%)
2 1 2 34 62
(2%) (1%) (2%) (34%) (61%)
46 (31%) 39 (26%) 26 (17%) 26 (17%) 3 (2%)
32 29 14 23 3
(32%) (29%) (14%) (23%) (3%)
4.4 (1.4) 4.0 1Y7
4.3 (1.3) 4.0 2Y7
62% (41%) 80% 0%Y100%
64% (40%) 80% 0%Y100%
46% (37%) 50% 0%Y100%
49% (36%) 50% 0%Y100%
of hearing protection over the last 3 months. Regression analyses were also performed to evaluate the relationship between TFI and HHIA scores with the willingness-toaccept Gamma knife radiosurgery. Additionally, regression analyses were performed to evaluate the relationship between TFI and age, years as firefighter, and workrelated noise exposure. All correlations were weak and not statistically significant (p 9 0.05, data not shown).
DISCUSSION Tinnitus suppression resulting from long-term focal inactivation by infarction (9,10) and short-term inactivation
Hearing handicap by HHIA. Otology & Neurotology, Vol. 35, No. 6, 2014
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FIG. 3.
S. E. PROSS ET AL.
Tinnitus severity by TFI.
by neuromodulation of area LC (5,8) raise consideration for development of a noninvasive treatment tool to accomplish what invasive DBS has to offer: severity reduction that does not require active patient participation to manage acoustic devices or devotion of cognitive resources to behavioral therapies. Within this framework of nonauditory basal ganglia-based neuromodulation therapy for tinnitus, it should be recognized that DBS is reversible and titratable to optimize benefit, but SRS is both irreversible and nontitratable. Those 2 important disadvantages of SRS
FIG. 4.
compared with DBS may, however, be offset by the former treatment technique’s noninvasive approach. The principal goals of this pilot study were to perform a tradeoff analysis of willingness-to-accept novel therapy versus expected level of tinnitus improvement and to characterize tinnitus severity in the study cohort. Firefighters were chosen for this study as they experience significant intermittent noise exposure, which may put them at a higher risk for chronic tinnitus. They also represent a generally healthy cohort that could be extrapolated to the
Information about Gamma knife radiosurgery for tinnitus.
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TINNITUS AMONG FIREFIGHTERS
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Gamma knife radiosurgery to area LC of the caudate would be of interest to a large population of patients with moderate or lower tinnitus distress. Surveying San Francisco firefighters, this willingness-to-accept novel treatment study estimates that more than 40% would be at least ‘‘likely’’ to accept Gamma knife radiosurgery if 75% tinnitus improvement could be delivered. Should this innovative intervention be considered in the future, a rigorous clinical trial will be necessary to establish safety and efficacy. Acknowledgments: The authors thank Joanne Hayes-White, chief of the San Francisco Fire Department; Thomas O’Connor, president of San Francisco Firefighters Local 798; and all of the respondents for their collaboration and assistance. FIG. 5. Willingness-to-accept Gamma knife radiosurgery for tinnitus across decreasing levels of expected tinnitus improvement.
REFERENCES
wider population of tinnitus patients. This study found 64% of the respondents had no hearing handicap and 85% had a moderate or lesser problem with tinnitus. Self-reported work-related noise exposure and tinnitus distress level was uncorrelated. Remarkably, at the 75% level of expected tinnitus improvement, more than 40% would be ‘‘likely,’’ ‘‘very likely,’’ or ‘‘definitely’’ willing-to-accept Gamma knife radiosurgery. This indicates strong interest among tinnitus patients with relatively mild severity to consider a novel noninvasive therapy to suppress their auditory phantoms. In the subpopulation of more highly distressed tinnitus patients who seek treatment by an otologist or a hearing professional at a tinnitus clinic, they may be as willing, or possibly more willing, to accept Gamma knife radiosurgery. This hypothesis can be tested in a future study. As a pilot study with a relatively small sample size using an opportunity sampling procedure, the results are subject to a number of limitations. First, this anonymous survey has a relatively low response rate of 18.6% and is susceptible to respondent bias. Extrapolation of prevalence data to the general population of firefighters may not be appropriate. Second, firefighters may be distinct from the general population. By the nature of their dangerous work, they may represent a group that is less risk averse and more willing-to-accept novel treatments than the general population. Third, the representation of potential Gamma knife radiosurgery treatment risks may be inadequate, thereby potentially impacting risk to benefit tradeoff attitudes among respondents. Fourth, virtually all anonymous survey instruments do not control for respondent mood and motivationVfactors that can also impact response data. Fifth, the sampling was geographically limited to an urban fire department in California. For a more comprehensive description of willingness-toaccept profile of Gamma knife radiosurgery for tinnitus, nationwide sampling would be necessary to capture data that span the entire spectrum of tinnitus distress severity. More highly distressed tinnitus patients may be more willing to accept SRS for tinnitus.
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