Distortion product otoacoustic emmissions in Ménière's disease.

Distortion product otoacoustic emissions (DPOAEs) are an objective, non-invasive measure for evaluating outer hair cell (OHC) activity. In this study DPOAEs were measured in 70 patients affected by Meniere's disease (MD). In addition 58 out of 70 patients performed both an audiometric threshold evaluation pre- and postglycerol administration (i.e. glycerol test) and DPOAEs pre- and post-osmotic drug assumption. The purpose of this combined form of testing was to explore the effects of glycerol on the active non-linear mechanisms of the cochlea. More than 60% of the ears with MD emitted DPOAEs despite the presence of an average hearing threshold level above 40 dB (HTL). Changes in the DPOAE baseline measures were observed in 32.4% of cases after glycerol administration. Patients were divided in four groups according to the different pattern of DPOAEs shown after the glycerol test. In particular, three-quarters of cases showed a significant increase in DPOAE amplitude, one-quarter of patients, who initially did not express DPOAEs, eventually did after intake of the osmotic agent, while no decreased DPOAEs were observed in these series. The different expressions of DPOAEs should be associated with the evolutive phases of MD. In addiction, elucidation of the relationship between DPOAEs and the stages of MD was an outcome of this test.