A Comparison of Distortion Product Otoacoustic Emission Properties in Ménière's Disease Patients and Normal-Hearing Participants.

OBJECTIVES: Postmortem examination of temporal bones of Ménière's disease patients consistently show dilated endolymphatic spaces of the inner ear, for which the term endolymphatic hydrops has been coined. During the past decade, magnetic resonance imaging techniques for the inner ear appeared, advancing the diagnosis of Ménière's disease. They require, however, a field-strength of at least 3 T, are costly and not universally available. Alternative, noninvasive, cost-effective tests with high sensitivity and specifity for endolymphatic hydrops are desirable. In this study, we test the suitability of distortion product otoacoustic emissions (DPOAEs) for endolymphatic hydrops detection. Previous measurements of the commonly recorded cubic DPOAEs mainly register cochlear hearing loss and are not specific for Ménière's disease. Simultaneous recordings of cubic and quadratic DPOAEs might be more suitable to detect endolymphatic hydrops, because both DPOAE orders react differently to changes of the cochlear operating point as they might occur in Ménière's disease patients.

DESIGN: Cubic and quadratic DPOAEs were recorded in normal-hearing participants (N = 45) and in the affected and unaffected ears of patients with a diagnosis of definite Ménière's disease (N = 32). First, to assess the integrity of DPOAE-generating mechanisms, cubic DPOAE-grams were obtained with primary tone frequencies f2 between 1 and 8 kHz with primary tone levels l1 = 60 dB SPL and l2 = 50 dB SPL, and a fixed primary tone frequency ratio of 1.22. Then, cubic and quadratic DPOAEs were simultaneously recorded with primary tone levels l1 = l2 = 65 dB SPL and at primary tone frequencies f2 = 4 and 5 kHz, where f1 was successively varied such that the ratio f2/f1 ranged between 1.1 and 1.6 in 0.04 steps while quadratic and cubic DPOAE levels were extracted from the same recording.

RESULTS: Cubic DPOAEs were significantly reduced in the affected ears of Ménière's disease patients, and slightly reduced in the unaffected ears of Ménière's disease patients, relative to the ears of normal-hearing participants. In contrast, no significant changes could be seen in quadratic DPOAEs across the ears of normal-hearing participants and Ménière's disease patients.

CONCLUSIONS: We could identify a relatively good preservation of quadratic DPOAE levels in relation to a reduction of cubic DPOAE levels as a potential noninvasive diagnostic approach in the early stage of suspected Ménière's disease. Future studies validating the differential diagnostic power of this parameter in control groups with nonhydropic forms of hearing loss are warranted.