Abnormal positive potentials in round window electrocochleography.

Objective: To describe an atypical waveform, termed an abnormal positive potential (APP), on round window electrocochleograms (RW ECochG) of children and to relate its occurrence to clinical history.

Study design: APPs were identified prospectively, and a retrospective analysis was made of these patients' clinical histories, audiograms, and auditory outcomes (hearing aid, cochlear implant, or nonauditory communication)

Setting: Tertiary referral teaching hospital, day surgery and clinics.

Patients: All 431 children <110 months of age suspected of a severe to profound hearing loss who underwent RW ECochG from January 1993 to August 1997.

Intervention: Diagnostic RW ECochG for auditory threshold estimation.

Main outcome measure: The presence on the RW ECochG of the APP: an early positive potential in the absence of a compound action potential (CAP).

Results: An APP was observed in 34 children. The APP was most marked in response to clicks and 8-kHz tones. The APP click threshold averaged 70 dB hearing loss. The brainstem evoked potential of these children showed an absence of waves, or a broad positive wave with no subsequent waves. Twenty-nine of 30 behavioral audiograms obtained were indicative of severe to profound hearing loss. Auditory outcomes were available from 26 children; 45% of them derived no help from a hearing aid, and 8 children received a cochlear implant. Clinical factors frequently associated with APP were prematurity in combination with kemicterus or hypoxia.

Conclusions: APP thresholds were lower than neural thresholds or behavioral thresholds. Children with APP need close follow-up, because half of those studied needed nonauditory strategies to develop effective communication.