Short-Term Changes of Hearing and Distortion Product Otoacoustic Emissions in Sudden Sensorineural Hearing Loss

Objectives: The function of outer hair cells can be measured objectively and noninvasively by distortion product otoacoustic emission (DPOAE). The aims of the study were to investigate the changes of DPOAE in the recovery course and to pursue the relationship between the changes of DPOAE and hearing improvement in patients with sudden sensorineural hearing loss. Study Design: Retrospective case series review. Methods: Both DPOAE and pure tone audiometry were performed before 7 days after the onset and followed after 2 weeks in 40 patients with sudden sensorineural hearing loss. Patients were grouped on the basis of the initial hearing loss and the results of their recovery. All DPOAE amplitudes were analyzed at 2f1-f2, and DPOAE sum was calculated. Results: The initial DPOAE sum in ears with the initial mild-to-moderate hearing loss (hearing threshold, <= 55 dB) was not different from that in contralateral normal ears, but it was decreased or absent in ears with the initial moderately severe to profound hearing loss (hearing threshold, >55 dB) compared with that in contralateral normal ears. In ears with the initial moderately severe to profound hearing loss, the changes of DPOAE sum values positively correlated with the hearing improvement but not in ears with the initial mild-to-moderate hearing loss. Although the presence of initial DPOAE responses indicated good prognosis, the absence of initial DPOAE responses did not always indicate poor prognosis. Conclusion: Our findings showed that the function of outer hair cells is relatively spared in ears with the initial mild-to-moderate hearing loss, and its recovery is not related to the hearing improvement; however, the function of outer hair cells is impaired in ears with the initial moderately severe to profound hearing loss, and the functional improvement of outer hair cells is important for hearing recovery. Clinical implications of our findings were discussed.