Rule 3,000 for Screening Vestibular Schwannoma

Abstract

To the Editor: We are very grateful to the author(s) of this letter for taking the time to read and respond to our recent editorial (1). With all our respect, some of his arguments are good and deserve careful consideration, although we do not find them compelling. In fact, all our patients received both the hearing test (audiometry) and the reference standard test (magnetic resonance imaging [MRI]). There is no different disease, and the sample is the same. Magnetic resonance imaging was done when the hearing test responds to one of the definition of asymmetric sensorineural hearing loss reported in the literature. The 3,000-Hz frequency was not taken into consideration to decide if an MRI is needed. It is true that the performance of a diagnostic test will be distorted if its result influences whether patients undergo confirmation by the reference standard. This situation, sometimes called "verification bias" or "work-up bias" (2), would apply, for example, when patients with suspected coronary artery disease and positive exercise tests were more likely to undergo coronary angiography (the reference standard) than those with negative exercise tests. In fact, when we did the audiogram and we suspected an asymmetric hearing loss independent of the definition, we asked for MRI. Although audiogram is the first line to exceed, we cannot consider the audiogram as the diagnostic test for vestibular schwannoma (VS); therefore, the verification bias was not violated. However, there is no bias, and we do not agree with the author of this letter. The rule 3,000 is valid for our sample and does not represent the population. The limitation of our study, already mentioned in our article, is the limited number of our sample and the important number of VS referred cases. We are processing a study with a larger number of patients from a population who seeks first-line care by the general practitioner instead of referred patients to a specialized care facility in otolaryngology, and results are promising. A comparison of the different existing definition and the rule 3,000 definition was done. Fortunately, the rule 3,000 shows its superiority to the other definition in terms of sensitivity and specificity. Results will be published shortly. In addition, the 3,000-Hz frequency shows its superiority to the other frequencies and to the speech discrimination level. All MRIs were done independently of the 3,000-Hz asymmetry. Retrospectively, during the analysis of our data, we identified that the rule 3,000 alone is simple, practical to use in our daily consultation screening, and a superior criterion to suspect VS, and MRI is therefore needed. Isaam Saliba, M.D. Department of Otorhinolaryngology Head and Neck Surgery Centre Hospitalier de l'Université de Montréal Montreal University Montreal, Quebec, Canada Geneviève Martineau Centre Hospitalier de l'Université de Montréal Montreal University Montreal, Quebec, Canada Miguel Chagnon, M.Sc. Department of Statistics Montreal University Montreal, Quebec, Canada