Electrocochleographic study of experimentally induced endolymphatic hydrops

Area of Science:

• Otorhinolaryngology
• Neuroscience
• Auditory Physiology

Background:

• Endolymphatic hydrops is a condition characterized by excess fluid in the inner ear.
• It is associated with hearing loss and vestibular symptoms.
• Electrocochleography (ECoG) is a diagnostic tool used to assess inner ear function.

Purpose of the Study:

• To investigate the electrophysiological changes in guinea pigs with induced endolymphatic hydrops.
• To correlate these changes with the duration of hydrops.
• To evaluate the utility of ECoG in detecting hydrops-related auditory dysfunction.

Main Methods:

• Endolymphatic hydrops was induced in guinea pigs by obliterating the endolymphatic sac.
• Electrocochleography was performed at 1, 2, 4, and 8 months post-induction.
• Electrodes were placed at the apex and near the round window to record compound action potential (AP) and summating potential (SP).

Main Results:

• Initially (1 month), AP thresholds and amplitude growth were normal despite hydrops.
• Progressive increases in AP threshold (10-40 dB) and signs of recruitment were observed at 2, 4, and 8 months.
• Enhanced apical SP was noted at 1-2 months, with a tendency to decrease later; round window recordings showed minimal changes.
• Waveform deviations between AP and SP occurred in 69% of animals.

Conclusions:

• Induced endolymphatic hydrops leads to progressive auditory dysfunction detectable by ECoG.
• Changes in AP and SP, particularly at the apex, reflect the severity and duration of hydrops.
• ECoG is a valuable tool for monitoring hydrops progression and associated hearing loss.