Researchers at University of Colorado School of Medicine may have figured out what causes Meniere’s disease and how to attack it. According to Carol Foster, MD, from the department of otolaryngology and Robert Breeze, MD, a neurosurgeon, there is a strong association between Meniere’s disease and conditions involving temporary low blood flow in the brain such as migraine headaches.
Meniere’s affects approximately 3 to 5 million people in the United States. It is a disabling disorder resulting in repeated violent attacks of dizziness, ringing in the ear and hearing loss that can last for hours and can ultimately cause permanent deafness in the affected ear. Up until now, the cause of the attacks has been unknown, with no theory fully explaining the many symptoms and signs of the disorder.
“If our hypothesis is confirmed, treatment of vascular risk factors may allow control of symptoms and result in a decreased need for surgeries that destroy the balance function in order to control the spell” said Foster. “If attacks are controlled, the previously inevitable progression to severe hearing loss may be preventable in some cases.”
Foster explains that these attacks can be caused by a combination of two factors: 1) a malformation of the inner ear, endolymphatic hydrops (the inner ear dilated with fluid) and 2) risk factors for vascular disease in the brain, such as migraine, sleep apnea, smoking and atherosclerosis.
The researchers propose that a fluid buildup in part of the inner ear, which is strongly associated with Meniere attacks, indicates the presence of a pressure-regulation problem that acts to cause mild, intermittent decreases of blood flow within the ear. When this is combined with vascular diseases that also lower blood flow to the brain and ear, sudden loss of blood flow similar to transient ischemic attacks (or mini strokes) in the brain can be generated in the inner ear sensory tissues. In young people who have hydrops without vascular disorders, no attacks occur because blood flow continues in spite of these fluctuations. However, in people with vascular diseases, these fluctuations are sufficient to rob the ear of blood flow and the nutrients the blood provides. When the tissues that sense hearing and motion are starved of blood, they stop sending signals to the brain, which sets off the vertigo, tinnitus and hearing loss in the disorder.
Restoration of blood flow does not resolve the problem. Scientists believe it triggers a damaging after-effect called the ischemia-reperfusion pathway in the excitable tissues of the ear that silences the ear for several hours, resulting in the prolonged severe vertigo and hearing loss that is characteristic of the disorder. Although most of the tissues recover, each spell results in small areas of damage that over time results in permanent loss of both hearing and balance function in the ear.
Since the first linkage of endolymphatic hydrops and Meniere’s disease in 1938, a variety of mechanisms have been proposed to explain the attacks and the progressive deafness, but no answer has explained all aspects of the disorder, and no treatment based on these theories has proven capable of controlling the progression of the disease. This new theory, if proven, would provide many new avenues of treatment for this previously poorly-controlled disorder.
Many disorders of the inner hear which affect both hearing and balance can be hugely debilitating and are currently largely incurable. Cochlear implants have been used for many years to replace lost hearing resulting from inner ear damage. However, to date, there has not been an analogous treatment for balance disorders resulting from inner ear disease. One potential new treatment is an implantable vestibular prosthesis which would directly activate the vestibular nerve by electrical stimulation. This prosthetic treatment is tested in a new study by Christopher Phillips and his colleagues from the University of Washington in Seattle, USA. Their findings are published in the Springer journal Experimental Brain Research.
Meniere’s disease is a disorder of the inner ear that can affect hearing and balance to varying degrees. The characteristic symptoms are episodes of vertigo, tinnitus, a feeling of pressure in the ears and hearing loss which tends to worsen as time goes on. Although there is medication which can help once an attack is underway, there is currently no long-term therapy which can resolve the disease completely.
Phillips and his colleagues have developed a vestibular prosthesis which delivers electrical stimulation to the fluid inside the semi-circular canals of the ear. In effect, the stimulation of the fluid makes the brain believe that the body is moving or swaying in a certain direction. This then causes a compensatory postural reflex to stabilize the posture thereby helping to restore balance.
For their study, this prosthesis was inserted into the ears of four subjects all suffering from long-term Meniere’s disease and differing degrees of hearing loss which was resistant to other management strategies. After a full evaluation of each participant’s vestibular function, their eye function was measured in response to electrical stimulation along with their postural response both with their eyes open and closed.
The researchers found that electrical stimulation of the fluid in the semicircular canals of the affected ear did result in a change in posture, the direction of which was dependent on which ear was stimulated. However, each subject had different sway responses to the stimulation given. The authors believe this could be caused by small differences in the location of the electrode between subjects. Thus fine tuning and individual calibration for each electrode implant would be required for it to be effective.
Overall the results illustrate that this type of prosthesis may eventually be a possible treatment for balance issues caused by Meniere’s disease. However, there are a large number of matters which would need resolving before it is ready for use. The lack of consistency in direction and magnitude of sway response would require further study to ensure that any prosthesis developed could give reliable results for different individuals.
The authors conclude: “Taken together, our findings support the feasibility of a vestibular prosthesis for the control of balance and illustrate new challenges for the development of this technology. This study is a first step in that direction.”
Provided by Springer