Intratympanic gentamicin is used to control episodic vertigo in patients with the severe form of Meniere’s disease, but it may also cause hearing loss. The purpose of this study was to investigate gentamicin-induced changes in hearing in such patients.

In this study, a total of 38 patients (mean age 55.4 y, range 23–86 y, male 16, female 22, side rt 17, lt 21) who received intratympanic gentamicin administration were monitored by pure-tone audiogram (PTA) and click-evoked extratympanic electrocochleography (ECoG) over a period of five years. Hearing detection thresholds were measured by PTA, and the summating potential (SP), action potential (AP) and SP/AP ratio were determined by ECoG. The patients received dilute gentamicin solution with sodium bicarbonate administration into the middle ear 1 or 2 times.

The mean hearing level at mid frequencies (500–2000 Hz) was 47 dB before the treatment and 40 dB after the treatment. The mean hearing gains at the frequencies of 125, 250, 500 Hz, and 1 kHz were 12.6, 12.1, 10.5, and 6.2 dB, respectively. The differences in the hearing levels at the frequencies of 125, 250, and 500 Hz recorded before and after treatment were statistically significant (p<0.001).

The longitudinal follow-up conducted after the treatment did not show any worsening of the hearing levels or relapse of the vestibular symptoms. The SP/AP ratio (0.49 before and 0.34 after treatment) seemed to return to normal in the long term after gentamicin treatment. Normalized SP/AP resulted in hearing gain at the frequencies of 250 and 500 Hz. The amplitudes of the SP (0.59 before and 0.3 after treatment), and especially of the AP (1.23 before and 0.86 after treatment), decreased after gentamicin treatment, indicating hearing loss. The hearing was better in 16 cases (42%) and showed no change in 18 cases (47%), while hearing loss occurred in 4 cases (11%) because of gentamicin.

Intratympanic gentamicin treatment alleviated hearing loss and reduced vertigo. It also normalized the SP/AP ratio, and the consequent hearing gain may reflect a reduction in endolymphatic hydrops. Long-term observation after gentamicin treatment revealed stable hearing.