American Journal of Epidemiology Advance Access originally published online on August 30, 2006
American Journal of Epidemiology 2006 164(7):706; doi:10.1093/aje/kwj290
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Letter to the Editor |
RE: "EXPOSURE TO LOUD NOISE AND RISK OF ACOUSTIC NEUROMA"
Department of Neurosurgery, Lund University Hospital, S-221 85 Lund, Sweden
(e-mail: carl-henrik.nordstrom{at}med.lu.se)
I read the article by Edwards et al. (1
) with interest—and increasing concern. The authors conclude that loud noise exposure is a risk factor for "acoustic neuroma" (vestibular schwannoma). Whether right or wrong, their conclusion may lead to social consequences: If the tumor is considered to be occupationally acquired, the demands for economic compensation will increase. It is also important that a revolutionary hypothesis regarding tumorigenesis have a solid scientific base.
Many high-quality scientific journals rightly emphasize the importance of adequate—sometimes quite complicated—statistical processing of the data presented. The quality of the statistics is, however, not always paralleled by a high quality of the biologic background. In their study, Edwards et al. (1) correctly point out an important potential bias. Since unilateral hearing loss is a frequent early symptom, patients who have developed the tumor might have focused on loud noise as a possible explanation for their disease. Obviously, the study should have been completed with objective data documenting that the tumor group actually had been more exposed than the control group. The accepted damage caused by loud noise is a quite characteristic change of the audiogram, and since the tumors in the study were unilateral and since both ears are usually simultaneously exposed, a simple hearing test could have answered this crucial question.
In the study, exposure to loud noise was defined as that exceeding a level of 80 decibels (approximately corresponding to the noise from an ordinary vacuum cleaner). Using this cutoff level for loud noise, the authors found the highest odds ratio for the development of "acoustic neuromas" among females (for 
15 years of exposure, odds ratio = 3.34, 95 percent confidence interval: 1.32, 8.43), several of whom had been exposed to "screaming children, sports events, and/or restaurants/bars" (1, p. 330). A hypothesis proposing that these levels of exposure lead to the development of tumors should have a very solid biologic background.
As we noted above, "acoustic neuroma" should correctly be termed "vestibular schwannoma." More than 90 percent of these tumors originate within the internal meatus from Schwann cells surrounding not the acoustic nerve but the superior vestibular nerve. There is no obvious relation between the stimulus of sound and the development of a tumor in fairly distant cells surrounding a nerve that has nothing to do with hearing. The only connection is the unfortunate, outdated term "acoustic neuroma." The entire paragraph "Acoustic trauma and tumorigenesis," which correctly describes some cellular effects and damage occurring within the cochlea upon exposure to loud noise, bears no relation to the development of vestibular schwannomas and contributes to complete biologic confusion. I doubt very much that the Journal would have accepted similar statistical nonsense.
The article by Edwards et al. is an example of the fact that a statistically verified correlation does not constitute a sufficient foundation for a scientific conclusion—there must also be a reasonable theoretical explanation (2).
ACKNOWLEDGMENTS
Conflict of interest: none declared.
References
- Edwards CG, Schwartzbaum JA, Lönn S, et al. Exposure to loud noise and risk of acoustic neuroma. Am J Epidemiol 2006;163:327–33.
[Abstract/Free Full Text] - Leibovici L. Effects of remote, retroactive intercessory prayer on outcomes in patients with bloodstream infection: randomized controlled trial. BMJ 2001;323:1450–1.
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  C. G. Edwards, J. A. Schwartzbaum, S. Lonn, A. Ahlbom, and M. Feychting THE AUTHORS REPLY Am. J. Epidemiol., October 1, 2006; 164(7): 706 - 707. [Full Text] [PDF]
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