Tehran University Medical Journal (Apr 2007)
Clinical and audiological features of a syndrome with deterioration in speech recognition out of proportion to pure hearing loss
Abstract
Background: The objective of this study was to describe the audiologic and related characteristics of a group patient with speech perception affected out of proportion to pure tone hearing loss. A case series of patient were referred for evaluation and management to the Hearing Research Center.To describe the clinical picture of the patients with the key clinical feature of hearing loss for pure tones and reduction in speech discrimination out of proportion to the pure tone loss, having some of the criteria of auditory neuropathy (i.e. normal otoacoustic emissions, OAE, and abnormal auditory brainstem evoked potentials, ABR) and lacking others (e.g. present auditory reflexes). Methods: Hearing abilities were measured by Pure Tone Audiometry (PTA) and Speech Discrimination Scores (SDS)), measured in all patients using a standardized list of 25 monosyllabic Farsi words at MCL in quiet. Auditory pathway integrity was measured by using Auditory Brainstem Response (ABR) and Otoacoustic Emission (OAE) and anatomical lesions Computed Tomography Scan (CT) and Magnetic Resonance Image (MRI) of brain and retrocochlea. Patient included in the series were 35 patients who have SDS disproportionably low with regard to PTA, absent ABR waves and normal OAE. Results: All patients reported the beginning of their problem around adolescence. Neither of them had anatomical lesion in imaging studies and neither of them had any finding suggestive of conductive hearing lesion. Although in most of the cases the hearing loss had been more apparent in the lower frequencies (i.e. 1000 Hz and less), a stronger correlation was found between SDS and hearing threshold at higher frequencies. These patients may not benefit from hearing aids, as the outer hair cells are functional and amplification doesn’t seem to help; though, it was tried for all. Conclusion: These patients share a pattern of sensory –neural loss with no detectable lesion. The age of onset and the gradual deterioration are remarkable. It seems that this is a new category of sensory –neural haring loss which deserves more attention.
