The evidence of noninner ear involvement in the presence of depressed bone conduction threshold at 2 kHz frequency

Abstract

Pure-tone audiometry is a standard clinical test for hearing diagnosis. Air–bone gaps derived from the difference between air conduction (AC) and bone conduction (BC) thresholds are important indicators to distinguish between different types of hearing losses. Even though BC thresholds are typically unaffected in conductive hearing loss (CHL) cases, a notch or depression at 2 kHz frequency (i.e., Carhart notch) could occur, which could be mistakenly considered as the involvement of sensorineural hearing loss (SNHL). In this article, it was clearly demonstrated that the BC notch at 2 kHz (that could exceed the normal limit) was in fact related to CHL (not SNHL). That is, in this case, both AC and BC thresholds became “perfectly” normal after the treatment (and the notch at 2 kHz disappeared). Several useful points were highlighted from the present case report to guide clinicians, medical trainees, and respective students to avoid misdiagnosis in clinical practice.