LETTERS TO THE EDITOR
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To the Editor:
The American College of Occupational and Environmental Medicine in September 2018 updated its Guidance Statement on Occupational Noise-Induced Hearing Loss.1 Previous versions had been published in 20032 and 2012.3 The typical appearance of the audiogram in noise-induced hearing loss (NIHL) is described in this way: “Its first sign is a ‘notching’ of the audiogram at the high frequencies of 3000, 4000, or 6000 Hz with recovery at 8000 Hz.”1 However, none of the Guidance Statements go beyond this general description and provide specific, objective criteria for detecting an audiometric notch.
Three points deserve to be made. The first point is that the lack of specific, objective criteria for detecting an audiometric notch has been shown to lead to substantial variation (from 35% to 65%) in the rate of detection of notches between experts who performed independent interpretations of a series of audiograms.4 The authors stated that, “The main problem here seems to be that there is no standard definition of an audiometric notch, so people tend to develop their own criteria.” To the extent that the presence of an audiometric notch is considered vital to the diagnosis of NIHL, the rate of diagnosis of that condition will vary widely between audiogram interpreters.
Secondly, the lack of specific, objective criteria for detection of an audiometric notch leads to intrainterpreter variation in the rate of detection of notches such that experts reading audiograms twice in a blinded manner agreed with themselves only 55% to 90% of the time.5 The authors concluded that “some experts were not internally consistent in their judgements about either the presence of a notch or of notch progression.” The authors called for further research that could lead to an “industry-wide standard” definition of an audiometric notch. To the best of my knowledge, such research has not been published, although various objective criteria for audiometric notches exist.6–11
The third point is the lack of specificity of the audiometric notch for the diagnosis of NIHL. Audiometric notches are commonly found in workers without significant occupational or non-occupational noise exposure.12–16 Nondahl et al13 stated that “notches can occur in the absence of a positive noise history” and found that individuals with a history of occupational noise exposure were only 8% to 36% more likely to have audiometric notches than those without such exposure. As stated by Lie et al,12 “The prevalence of Coles notch and notch index in the present study is approximately 60% in the exposed and 50% in the nonexposed group. This implies that the specificity of one notch as criterion for NIHL diagnosis is very low, as 5 of 6 notches may be unrelated to occupational noise exposure. The general rule that a hearing loss with a notch indicates an NIHL and the lack of a notch speaks against must be used with great caution.”
An “industry-wide standard” definition of an audiometric notch is urgently needed to help make the diagnosis of NIHL more consistent. Research into the possible causes of audiometric notches in individuals without noise exposure is also needed. Perhaps American College of Occupational and Environmental Medicine, in cooperation with other professional organizations involved in hearing conservation, will support the necessary research.
1. Mirza R, Kirchner DB, Dobie RA, Crawford J. ACOEM task force on occupational hearing loss, acoem guidance statement occupational noise-induced hearing loss. J Occup Environ Med
2. Kirchner DB, Evenson E, Dobie RA, et al. ACOEM guidance statement. Occupational noise-induced hearing loss. J Occup Environ Med
3. American College of Occupational and Environmental Medicine. ACOEM evidence-based statement: noise-induced hearing loss. J Occup Environ Med
4. McBride DI, Williams S. Audiometric notch as a sign of noise induced hearing loss. Occup Environ Med
5. Rabinowitz PM, Galusha D, Slade MD, Dixon-Ernst C, Sircar KD, Dobie RA. Audiogram notches in noise-exposed workers. Ear Hear
6. Coles RR, Lutman ME, Buffin JT. Guidelines on the diagnosis of noise-induced hearing loss for medicolegal purposes. Clin Otolaryngol Allied Sci
7. McBride DI, Williams S. Characteristics of the audiometric notch as a clinical sign of noise exposure. Scan Audiol
8. Niskar AS, Kieszak SM, Holmes AE, Esteban E, Rubin C, Brody DJ. Estimated prevalence of noiseinduced hearing threshold shifts among children 6 to 19 years of age: the Third National Health and Nutrition Examination Survey, 1988–1994, United States. Pediatrics
9. Dobie RA, Rabinowitz PM. Change in audiometric configuration helps to determine whether a standard threshold shift is work-related. Spectrum
10. Hoffman HJ, Lo CW, Themann CL, Dillon CF, Franks JR. Reducing noise-induced hearing loss (NIHL) to achieve U.S. Healthy People 2010 goals. Am J Epidemiol
11. Wilson RH. Some observations on the nature of the audiometric 4000 Hz notch: data from 3430 veterans. J Am Acad Audiol
12. Lie A, Skogstad M, Johnsen TS, Engdahl B, Tambs K. The prevalence of notched audiograms in a cross-sectional study of 12,055 railway workers. Ear Hear
13. Nondahl DM, Shi X, Cruickshanks KJ, et al. Notched audiograms and noise exposure history in older adults. Ear Hear
14. Osei-Lah V, Yeoh LH. High frequency audiometric notch: an outpatient clinic survey. Int J Audiol
15. Lie A, Skogstad M, Johnsen TS, Engdahl B, Tambs K. A cross-sectional study of hearing thresholds among 4627 Norwegian train and track maintenance workers. BMJ Open
16. Lie A, Engdahl B, Hoffman HJ, Chuan-Ming L, Tambs K. Occupational noise exposure, hearing loss, and notched audiograms in the HUNT Nord-Trøndelag Hearing Loss Study, 1996–1998. Laryngoscope