Distortion product otoacoustic emissions as a prognostic factor for idiopathic sudden sensorineural hearing loss

We investigated distortion product otoacoustic emissions (DPOAE) as a prognostic factor in idiopathic sudden sensorineural hearing loss (ISSHL) patients with the time-dependent Cox proportional-hazards model. We also compared the importance of the prognostic factors that are reported in the literature. 108 patients with ISSHL were included. Both DPOAE and pure tone audiometry were performed everyday for a maximum of 7 days during admission and followed every other week or monthly after discharge. All DPOAE amplitudes were analyzed at 2f1-f2--namely 1093, 1375, 1750, 2187, 2781, 3500, 4375, and 5500 Hz. The average of two series of DPOAE intensity corrected for the noise level in eight frequencies was coded as dichotomous at > or =6 or <6 dB. We selected the most updated DPOAE at 3 days or more before the assessment of recovery into the analysis. The potential confounders including age, sex, history of vertigo at onset, history of hypertension, diabetes, coronary arterial disease, and stroke, configuration and severity of initial pure tone audiometry, the duration from onset to treatment, auditory brainstem response (ABR), vestibular evoked myogenic potential (VEMP), and plasma triglyceride and cholesterol levels, hemoglobin level, and erythrocyte sedimentation rate were collected for evaluation. The results showed that a better DPOAE amplitude was a significantly good prognostic indicator both in univariate analysis (recovery rate ratio = 3.626, 95% CI = 2.119-6.205, p < 0.0001) and multivariate analysis (recovery rate ratio = 2.94, 95% CI = 1.537-5.624, p = 0.0011). The Kaplan-Meier estimates showed that the younger age group (< or =40 years) with better initial pure tone audiometry (<65 dB) represented a better prognosis that was compatible with previous literature (log-rank test, p = 0.0297 and p = 0.0019 respectively). In the univariate analysis, normal ABR and VEMP waveforms were associated with a better prognosis (ABR: recovery rate ratio = 2.984, 95% CI = 1.742-5.112, p < 0.0001; VEMP: recovery rate ratio = 1.978, 95% CI = 1.183-3.305, p = 0.0093). The configuration of initial audiometry was also a significant prognostic factor that patients with scale-out type (recovery rate ratio = 0.228, 95% CI = 0.089-0.584, p = 0.002) and tent type (recovery rate ratio = 0.081, 95% CI = 0.008-0.778, p = 0.0295) were associated with a poorer prognosis than those with the flat type in the multivariate analysis. In this study, the time-dependent Cox proportional-hazards model established the prognostic value of DPOAE for ISSHL patients. This model can also be used for comparison of different treatment protocols. In addition, the further development of a predictive model based on this method is worthy of being investigated.