内リンパ水腫の発症機序と内耳障害

抄録

Yamakawa first reported endolymphatic hydrops (EH) in a patient with Meniere’s disease (MD) in 1938. In the same year, Hallpike and Cairns also reported the association between MD and EH and established the modern diagnosis of MD. This association is now widely accepted; however, doubts have recently been raised. A recent human temporal bone study review failed to conclude if the association is an epiphenomenon or whether EH causes MD.

The mechanism of EH development remains enigmatically unclear. There is a large amount of evidence to suggest that water homeostasis in the inner ear is regulated partly via the vasopressin-aquaporin 2 (VP-AQP2) system, suggesting that EH reflects malregulation of the VP-AQP2 system in the inner ear fluid. Moreover, unfavorable development of the endolymphatic sac (ES) and duct and ES fibrosis have been reported in the temporal bones of MD patients. Based on these results, we hypothesized that a combination of ES dysfunction and dysregulation of endolymph might induce Meniere’s attacks.

Clinically, it is well known that Meniere’s attacks are related to stress. Moreover, the plasma level of VP, a stress hormone, is known to be increased in patients with MD. We recently developed an animal model that is better suited for studying MD, because this model consists of a combination of ES dysfunction and dysregulation of endolymph. In contrast to previous animal models that rarely showed episodes of imbalance, spontaneous nystagmus, or vertiginous attacks, even though they are distinct features of EH, they are evident in our model. Moreover, our model also shows hearing impairment.

In this paper, mechanisms underlying the formation of endolymphatic hydrops and its inner ear disorder the inner ear disorder associated with it are presented, mainly based on our recent studies.