Otoacoustic emissions for monitoring aminoglycoside-induced ototoxicity in children with cystic fibrosis.

OBJECTIVE To investigate whether transient-evoked and distortion-product (DP) otoacoustic emissions (OAEs) are more sensitive than pure-tone audiometry (PTA) in revealing gentamicin-induced ototoxicity in children with cystic fibrosis (CF). DESIGN Prospective case-control study. SETTING Tertiary referral audiologic center in conjunction with an academic pediatric CF unit. PARTICIPANTS The study group consisted of a consecutive sample of 12 audiologically normal children with CF and a history of gentamicin exposure (CF-gentamicin group). The control groups consisted of 8 age-matched children with CF and 11 age-matched healthy volunteers. No member of the control groups had a history of aminoglycoside exposure. INTERVENTION Members of the CF-gentamicin study group received 4 mg/kg of gentamicin per day for a mean of 14.2 days (range, 11-29 days). OUTCOME MEASURES The PTA thresholds (250-8000 Hz) were the criterion standard. Transient-evoked OAEs' reproducibility at 5 frequency bands (800, 1600, 2400, 3200, and 4000 Hz) and total emission level were measured, as were DP-audiogram (DP-gram) amplitude (1001-6299 Hz), input-output function dynamic range, and detection thresholds at 4004, 6006, and 7996 Hz. Baseline measurements were compared between groups examining the effect of CF and previous gentamicin exposure (2-way analysis of variance). For the CF-gentamicin group, baseline measurements were compared with those at the end of the last gentamicin treatment (paired t test). RESULTS The PTA findings were normal for all groups at baseline and remained normal in the CF-gentamicin group after treatment. The CF-gentamicin group had significantly lower transient-evoked OAEs total emission level, DP-gram amplitude at 5042 Hz, and input-output dynamic ranges with higher detection thresholds in all frequencies compared with both control groups, which was attributed completely to previous gentamicin exposure (P<.05). After treatment, further decreases in total emission levels, DP-gram amplitudes (>3000 Hz), and dynamic ranges were noted, with increased detection thresholds (P<.05). CONCLUSIONS Otoacoustic emissions measurement (especially of DP OAEs) proved more sensitive than PTA in revealing minor cochlear dysfunction after gentamicin exposure. They should be used for monitoring patients receiving ototoxic factors such as aminoglycosides.