Risk factors for loss of ipsilateral residual hearing after hybrid cochlear implantation

OBJECTIVE: Residual low-frequency acoustic hearing benefits cochlear implantees in difficult listening situations such as understanding speech in noise and music appreciation. Most subjects retain functional residual hearing in the operated ear. A small number of patients, however, will lose significant ipsilateral residual hearing after short-electrode cochlear implantation. The objectives of this retrospective series are to determine whether predisposition to hearing loss after implantation exists in a subset of patients and to assess the functional impact of this hearing loss on clinical measures of combined electric and acoustic hearing. STUDY DESIGN: Retrospective case series. SETTING: Multicenter clinical trial; tertiary care facility. PATIENTS: Hearing preservation cochlear implant recipients. MAIN OUTCOME MEASURE: Frequency-averaged ipsilateral hearing loss at 1 year after activation. RESULTS: Eighty-five patients from the Hybrid S8 FDA trial had serial postoperative audiometric measurements. Twenty-two of these patients, implanted at the home institution, provided additional medical data. Univariate analysis (Pearson's, Spearman's, Student's t test) showed that the severity of hearing loss at 1 year after activation was significantly correlated with age, male gender, and noise-induced hearing loss as the etiology of hearing impairment. A multivariate regression model corroborated these variables. No other medical factors were predictive. Clinical measures of speech perception (Consonant-Nucleus-Consonant and Hearing in Noise Test) worsened with hearing loss in ipsilateral but not bilateral listening conditions. CONCLUSION: Age, male gender, and a history of noise-induced hearing loss correlate with the severity of hearing loss at 1 year after activation. Even the most severely affected patients benefit from bilateral electric and acoustic inputs.