The Meniere attack: an ischemia/reperfusion disorder of inner ear sensory tissues

Abstract

We believe Meniere attacks arise as a chance association of endolymphatic hydrops and vascular risk factors for intracerebral ischemia. Hydrops acts as a variable Starling resistor upon the inner ear vasculature that is capable of inducing ischemic attacks only in people with reduced perfusion pressure in the ear. The unique characteristics of the attacks (loss of vestibular response and hearing acutely followed by a return to apparent normalcy over hours) are explained by the differential sensitivity of the inner ear tissues to transient ischemia, with the sensory tissues (dendrites, hair cells) vulnerable to hours-long ischemia/reperfusion injury, and the stria vulnerable to ischemia due to its high metabolic rate. Permanent hearing loss and vestibular damage after many attacks would result when small areas of irreversible sensory cell damage accumulate and become confluent. This theory is supported by the strong correlation of hydrops with Meniere attacks, the finding that autoregulation of cochlear blood flow is impaired in the hydropic ear, and studies demonstrating that symptoms and signs in people and in animal models vary with conditions that alter perfusion pressure in the inner ear. Induction of Meniere attacks in animal models requires both hydrops and a mechanism that reduces perfusion pressure, such as epinephrine injection or head dependency. There is a strong clinical association between Meniere attacks and disorders that increase the risk for cerebrovascular ischemia, such as migraine. The excitable tissues in the sensory structures have long been known to be more vulnerable to ischemia than the remaining aural tissues, and are now known to be vulnerable to excitotoxicity induced by ischemia/reperfusion. This correlates well with autopsy evidence of damage to dendrites and hair cells and with strial atrophy in late Meniere disease cases. If this hypothesis is confirmed, treatment of vascular risk factors may allow control of symptoms and result in a decreased need for ablative procedures in this disorder. If attacks are controlled, the previously inevitable progression to severe hearing loss may be preventable in some cases.