Meniere’s Syndrome: Are Symptoms Caused by Endolymphatic Hydrops?

Saumil N. Merchant, M.D.
Massachusetts Eye and Ear Infirmary, Department of Otology and Laryngology, Harvard Medical School, Boston, Massachusetts.

Last edited: August 23, 2006

Introduction

Historically, an inner ear problem called endolymphatic hydrops has been hypothesized as the mechanism for Meniere’s syndrome. The development of endolymphatic hydrops results from abnormal pressure fluctuations of a fluid called endolymph, which is located in a system of membranes called membranous labyrinth.

Normal membranous labyrinth.

When pressure increases, the membranes dilate like a balloon – the swelling is referred to as hydrops.

Dilated membranous labyrinth in Meniere’s syndrome (hydrops).

According to the central hypothesis, although a variety of factors have been proposed as leading to the development of endolymphatic hydrops including excessive endolymph production, decreased endolymph absorption by the endolymphatic sac, ionic imbalance, genetic abnormalities, viral infection, autonomic imbalance, dietary factors, autoimmune reactions, vascular irregularities, allergic responses, and others (Kiang, 1989; Schuknecht, 1993; Merchant et al, 1995; Nadol, 1999), it is the actual hydrops that generates the symptoms of Meniere’s syndrome.

Central hypothesis for Meniere’s syndrome (modified after Kiang, 1989). Many possible etiologic factors can lead to endolymphatic hydrops, which in turn generates the clinical symptoms.

Interestingly, the hypothesis of endolymphatic hydrops as the final common pathway for Meniere’s syndrome has not been proven conclusively. A recently published study (Merchant et al, 2005) tested this hypothesis where database records of human temporal bone cases with a clinical diagnosis of Meniere’s syndrome (28 cases) or a histopathological diagnosis of hydrops (79) were reviewed to determine the role of hydrops in the manifestation Meniere’s syndrome symptoms. If the central hypothesis was true, every case with Meniere’s syndrome should have hydrops and every case with hydrops should exhibit typical Meniere’s symptoms, unless the chain of neural events is interrupted.

Study Results

Every one of the 28 cases with Meniere’s disease had endolymphatic hydrops (in at least one ear) on histopathologic examination of the affected ear. However, the reverse was not true. Considering the hydrops cases, nine cases categorized as idiopathic hydrops and 10 cases categorized as secondary hydrops did not exhibit the classic symptoms of Meniere’s syndrome.

Discussion

The finding that endolymphatic hydrops was present in every case with a clinical diagnosis of Meniere’s syndrome establishes the correlation between Meniere’s syndrome and hydrops; however, the correlation does not imply a cause-and-effect relationship. If the central hypothesis was true, every Meniere’s syndrome case should have endolymphatic hydrops and every case of hydrops should have the clinical symptoms.

Thus the study results are not consistent with the central hypothesis that hydrops is the final common pathway for the manifestation of Meniere’s syndrome symptoms. Rather, the findings suggest that hydrops may be a marker for disordered homeostasis of the labyrinth, in which some factor (as yet unknown) produces the clinical symptoms of Meniere’s syndrome and endolymphatic hydrops.

Further research is needed to determine the cellular and molecular basis for Meniere’s syndrome symptoms since evidence suggests a cause other than hydrops. Therefore, medications aimed at alleviating hydrops are unlikely to control the disorder. A more complete understanding of the syndrome at a cellular level may provide insight into targets for novel therapeutic intervention.

Conclusion

Endolymphatic hydrops should be considered a histological marker for Meniere’s syndrome rather than a direct cause of associated symptoms. Medications aimed at alleviating hydrops are unlikely to control Meniere’s syndrome.

References

Kiang NYS. An auditory physiologist’s view of Meniere’s syndrome. In Nadol JB Jr, ed. Second International Symposium on Meniere’s disease. Amsterdam: Kugler & Ghedini, 1989:13-24.

Merchant SN, Adams JC, Nadol JB Jr. Pathophysiology of Meniere’s syndrome: are symptoms caused by endolymphatic hydrops. Otol Neurotol 2005; 26:74-81.

Merchant SN, Rauch SD, Nadol JB Jr. Meniere’s Disease. Eur Arch Otorhinolaryngol 1995;252:63-75.

Nadol JB Jr. Pathogenesis of Meniere’s syndrome. In Harris JP, ed, Meniere’s Disease. The Hague, The Netherlands: Kugler Publications, 1999: 73-9.

Schuknecht HF. Pathology of the Ear, 2nd ed. Philadelphia: Lea & Febiger, 1993.

Acknowledgments

• The above article was abridged with permission from Otology & Neurotology, Vol. 26, No. 1, pp: 74-81, 2005.
• Some of the material found in this site, including indicated graphics, was funded by a center grant from the National Institutes of Health. (NIH P60-DC02764). "National Multipurpose Research and Training Center." 12/01/1995-11/30/2000. The NIH is not responsible for the content, usage, or accuracy. Graphics so-marked may be used for noncommercial purposes, including use on the internet, with an acknowledgement to the source.