On a possible prognostic value of otoacoustic emissions: a study on patients with sudden hearing loss

Otoacoustic emissions (OAE) and pure tone audiogram (PTA) were examined in 26 ears of 25 patients suffering from sudden hearing loss from the 1st day to up to 505 days following the drop of hearing to test the hypothesis whether the OAEs are capable of delivering predictive information about the recovery process. The patients were selected from 50 candidates according to the following criteria: one or both ears exhibited a systematic and significant recovery of pure tone threshold in at least one frequency, OAEs were detectable and PTA available, a conductive hearing loss was excluded, and the auditory brainstem responses (ABR) yielded no signs of retrocochlear disorders. Transitory evoked otoacoustic emissions (TEOAE) and distortion product otoacoustic emissions (DPOAE) were measured under constant stimulus and recording conditions in three to nine sessions. The relation between OAE level and actual pure tone threshold was subject to a regression analysis. The correlation between both parameters is small but significant. Even smaller correlations are observed if the OAE level is related to former hearing loss, whereas the correlation improves if the OAE level is compared to the pure tone threshold measured in a later session. The slopes of individual trajectories that connect the successive results of one ear in a plane defined by hearing loss and OAE level show a remarkable accumulation around zero, i.e., in many cases the OAEs remain unchanged even if the hearing loss decreases. The comparison of the OAE levels measured at an early stage with later audiograms shows that there are only a small number of cases with small initial emissions and good final threshold or large initial emissions and bad final threshold. This means that small initial OAEs end up with a remaining final hearing deficit, whereas a high OAE level immediately after drop of threshold correlates with good outcome. The reliability of an individual prediction based on the OAE level combined with the threshold after sudden hearing loss and the consequences for the physiologic mechanisms underlying the sudden hearing loss remain to be proved in further investigations.