Discussion

This study identified 26 patients with sensorineural hearing loss featuring a high-pitch notched audiogram but no history of noise-induced hearing loss. The underlying cause of such presentation has been a longstanding enigma, at times being erroneously attributed to noise exposure even without any history of such.^{Reference Sataloff, Sataloff, Sataloff and Sataloff1} It is widely accepted that a diagnosis of noise-induced hearing loss cannot be made on the basis of the audiogram alone,^{Reference Sataloff, Sataloff, Sataloff and Sataloff1–Reference Luxon, Prasher and Luxon5} but it is not uncommon in otolaryngological practice to encounter such erroneous opinions.

There have been a few past reports of high-pitch notched audiograms in the absence of a history of noise exposure, mostly based on retrospective, non-clinical analysis of questionnaires, without the benefit of a detailed clinical history collected in a prospective manner. Lie et al.^{Reference Lie, Engdahl, Hoffman, Li and Tambs6} used data based on audiograms and questionnaires from a large population of hearing loss patients who were originally part of the Nord-Trøndelag Health Study. They found audiometric notches occurring in both noise-exposed and non-exposed residents. Nondahl et al.^{Reference Nondahl, Shi, Cruickshanks, Dalton, Tweed and Wiley7} used data from a population questionnaire-based study of older adults designed to evaluate published algorithms for identifying notched audiograms. In addition, they found that 11 per cent of participants had no history of exposure to noise. Osei-Lah and Yeoh^{Reference Osei-Lah and Yeoh8} retrospectively reported a group of patients attending an audiovestibular clinic with high-frequency audiometric notches that were not attributable to noise exposure.

Audiograms notched at 4 kHz have been described in association with clinical events such as viral infections,^{Reference Sataloff and Vassallo9} barotrauma, closed head injury, labyrinthitis, perilymph fistula,^{Reference Colvin, Luxon, Luxon and Prasher4} ototoxins,^{Reference Luxon, Prasher and Luxon5} and neonatal jaundice with kernicterus.^{Reference Sataloff, Sataloff, Sataloff and Sataloff10} Notches on audiograms at 6 kHz may be artefactual.^{Reference Lutman, Qasem, Prasher and Luxon11} Genetic causes, seen as familial high-pitch notched audiograms in the absence of noise exposure, have been demonstrated in two studies,^{Reference Klockhoff and Lyttkens12,Reference Oluwole and Irwin13} in addition to other observations.^{Reference Anderson and Wedenberg14–Reference Huizing, van Bolhuis and Odenthal16}

In considering the cause of these high-pitch notched audiograms, one could entertain the possibility that a history of past noise exposure may have simply been forgotten by patients. Whilst otic trauma and acoustic trauma events may be single and forgotten, noise-induced hearing loss is a gradual process, requiring a long time of repeated exposure, rather than a single or few salient events.^{2,Reference Dobie17–Reference Sataloff, Sataloff, Sataloff and Sataloff19} The benefit of this prospective clinical study has been the ability to thoroughly question the patient about possible past noise exposure at the time of clinical assessment; thus, it is very unlikely that a history of repeated causal exposure to noise over a long period of time leading to noise-induced hearing loss was not detected.

The concept of susceptibility (‘soft’ and ‘hard’ ears) does show variation in the effect of noise-induced hearing loss on ears.^{Reference Dobie20–Reference Sataloff, Sataloff, Sataloff and Sataloff23} However, as noted in the previous paragraph, this still requires a history of repetitive exposure over a long period of time that is unlikely to elude a detailed history in a prospective study, and no such history of repetitive noise exposure was found in this group. Such a concept of higher susceptibility does not therefore seem a tenable explanation in this group with high-pitch notched audiograms and a lack of any history of progressive noise exposure.