High frequency audiometric notch: an outpatient clinic survey.

It is a common misconception that high frequency audiometric notches are diagnostic of noise induced hearing loss. The aim of this study was to identify the prevalence of high frequency notch (HFN) in an audiovestibular medicine outpatient clinic population at a district general hospital. One hundred and forty nine consecutive adult patients were assessed. According to standard practice at the audiovestibular clinic, a full clinical history with particular emphasis on neuro-otological symptoms, noise exposure, and medical risk factors for sensorineural hearing loss was taken. After standard 8-frequency pure tone audiometry, subjects were divided into those with HFN and those without. There were 84 (56%) females and 65 (44%) males with a mean age of 45 years (range: 19 to 91 years). A total of 39.6% had notches not attributable to noise (occupational or recreational) or any other known risk factor. In 29 (49.2%) and 15 (25.4%) the HFN was present in the left and right ear respectively whereas 15 (25.4%) were bilateral. The frequency least affected was 3 kHz while 4 kHz and 6 kHz were affected in almost equal proportions. In 53 ears (71.6%), the notch depth was less than 20 dBHL (10-19 dB) compared to 21 ears (28.4%) with a depth of 20 dBHL or more. This study concludes that high frequency notch without excessive noise exposure or any other known factor is common. It is neither diagnostic of, nor invariable with NIHL unless a convincing history of hazardous noise exposure is elicited from the history.