Vestibular Evoked Myogenic Potentials and Distortion-Product Otoacoustic Emissions Combined with Glycerol Testing in Endolymphatic Hydrops: Their Value in Early Diagnosis

The present investigation was specifically designed to evaluate the ability of the glycerol test combined with pure tone audiometry, distortion-product otoacoustic emissions (DPOAEs), and vestibular evoked myogenic potentials (VEMPs) to diagnose endolymphatic hydrops early and to identify cases that may evolve toward Meniere's disease. This investigation consisted of 29 consecutive patients with mild dizziness or vertigo who received no treatment. Each patient underwent glycerol testing measured with conventional pure tone audiometry and with both DPOAEs and VEMPs. It is interesting to note that in 7 and 8 of the 29 cases, the VEMPs and DPOAEs, respectively, showed an improvement after glycerol administration that had not been shown on traditional audiometry. A further element worthy of consideration emerges from an analysis of the VEMP results compared to the DPOAE results that divided the patients into 4 groups. The first group had a postglycerol improvement with both methods, which would seem to suggest hydrops in both the anterior and posterior parts of the labyrinth. In the second and third groups, there was an improvement only either with VEMPs or DPOAEs, and this finding seems to indicate that only one endolymphatic compartment might be involved. In the last group, all patients had a positive glycerol test with positive DPOAEs on one side and with positive VEMPs on the other. Although endolymphatic hydrops can only be proven after death, a combination of VEMPs and DPOAEs with the glycerol test may permit early diagnosis of endolymphatic hydrops. These results clearly imply that these methods should be permanently included in the diagnostic protocol of patients with vestibular and audiological symptoms.