Hydrocortisone applied into the round window niche causes electrophysiological dysfunction of the inner ear.

A suspension of 2% hydrocortisone, micronized in sterile water, was instilled through a perforation in the tympanic membrane into the round window (RW) niche of 9 healthy rats once a day for 5 consecutive days. Three animals were used as controls, and were exposed to sterile water only instilled into the RW niche. Auditory brainstem response (ABR) thresholds were determined for eight frequencies: 2, 4, 6, 8, 12, 16, 20 and 31.5 kHz. Hydrocortisone caused impaired ABR thresholds in the frequency range of 12-31.5 kHz after 5 days of instillation. The impaired thresholds remained unchanged for 2 months, indicating irreversible electrophysiological changes in the inner ear. No morphological damage could be detected in the cochlea by means of light microscopy or transmission electron microscopy. However, hydrocortisone delayed the healing of the perforated tympanic membrane.