Meniere’s Disease
In 1861, Prosper Meniere described this disorder which is characterized by a constellation of symptoms, including fluctuating hearing level, a sensation of fullness in the ear, roaring ringing in the affected ear, and episodic vertigo. There is usually a low tone hearing loss which fluctuates unpredictably. A sensation of fullness in the ear or a sensation that the ear is clogged is also not uncommon. The roaring tinnitus is usually of a low tone quality typically described as "ocean waves crashing along the beach".
Vertigo is a sensation of surrounding objects spinning around you or that you are physically being spun around. These spells come about at unpredictable times with no warning and last from several hours to days. It is not uncommon for these spells to be associated with nausea and vomitting. The frequency of these attacks can vary from once a year to three times a day.
Pertinent Anatomy
Before we embark on further discussion, it is prudent to review and understand pertinent anatomy of the hearing and balance system.
Sound entering the ear canal causes vibrations of the tympanic membrane (eardrum). The eardrum is attached to one of three ossicles (bones) found in the middle ear, called the malleus. The malleus bone transmits the mechanical vibrations to another ossicle, the incus, which in turn transmits the vibrations to the smallest of the three ossicles, the stapes. The stapes bone vibrates and sends the message to the inner ear. The inner ear is made of a bony labyrinth filled with fluid and membranes. As the stapes vibrates, the fluid in the inner ear is set into motion. The cilia (hairs) on the ends of hair cells within the inner ear are bent and an electrical signal is generated and travels along the (cochlear) hearing nerve and then back to the brain. The inner ear is composed of the cochlea, which is responsible for hearing and the semicircular canals which convey balance information concerning angular acceleration of the head back to the brain. Two other organs, the saccule and utricle, found in the inner ear report on the linear acceleration of the head.
The internal auditory canal is the bony canal which encases the hearing and balance nerves on their way from the inner ear to the brain. Joining theses nerves in the canal is the facial nerve, which is responsible for allowing motion on that side of the face. This is the nerve that is responsible for our ability to raise our eyebrows, close our eyes, flare our nostrils and raise the corner of the mouth on that side. It is also responsible for transmitting information regarding taste from the front 2/3 of the tongue and for producing tears from the lacrimal glands in our eyes.
The inner ear (cochlea and semicircular canals ) is composed of two types of fluid called the endolymph and the perilymph. They differ in their sodium and potassium content and this difference in composition is what is responsible for the electrical charge of the inner ear.
The endolymph is formed within the cochlea and circulates throughout the inner ear. An extension of the inner ear, known as the endolymphatic duct and sac, lies against the dura or covering of the brain. Within the endolymphatic sac, endolymph is filtered through to the connective tissue around the sac. From here the fluid can enter blood vessels or enter the spinal fluid space. The volume of endolymph in the inner ear is extremely small and is measured in nanoliters.
Endolymphatic hydrops
When the endolymphatic sac becomes dysfunctional, fluid begins to accumulate within the inner ear and the endolymphatic sac. It is thought that as the fluid begins to accumulate, the symptoms of episodic vertigo, tinnitus, fullness in the ears, and fluctuating hearing level appear.
The term endolymphatic hydrops refers to a state of excessive fluid within the endolymphatic space. Endolymphatic hydrops can be caused by a number of diseases that can affect the rest of the body. These include metabolic disorders such as diabetes, low or over-active thyroid functioning, high cholesterol or triglyceride levels. There are a number of autoimmune and infectious disorders which can also cause these symptoms. The term "Meniere’s syndrome" refers to the constellation of symptoms including fluctuating hearing levels, sensation of fullness in the ears, roaring tinnitus and episodic vertigo. Technically the term "Meniere’s disease" refers to endolymphatic hydrops for which no other cause can be found.
Atypical Meniere’s Disease
When only some of the symptoms of Meniere’s disease are present, the condition is referred to as atypical Meniere’s disease. For example the episodes of vertigo may occur without any hearing abnormality or vice versa.
Diagnostic Evaluation
Beyond a thorough history and physical examination, some diagnostic tests can be of some value.
Blood tests to rule out thyroid dysfunction, diabetes, high cholesterol, syphilis and autoimmune disorders are helpful. Other tests which can provide additional evidence for Meniere’s disease include an audiogram (hearing test), an electronystagmogram (ENG, balance test), an electrocochleogram (ECoG), an auditory brainstem response (ABR) and a magnetic resonance image (MRI). An audiogram is a hearing test conducted in a sound-proof room by a qualified audiologist.
An electronystagmogram (ENG) is a balance test which involves placement of recording electrodes around the eyes. Movements of the eyes are recorded while changing positions of the head with respect to the earth’s gravitational field. The eye movements are also recorded while cool and warm air or water is blown into the ear canal. The semicircular canals of the inner ear are sensitive to changes in temperature. When the inner ear is cooled or warmed, the effect is to lessen or heighten activity within the horizontal semircular canal of the inner ear. The normal response is to feel vertigo during changes in temperature. The level of response to cool and warm stimuli is compared to the other ear. There is confirmatory evidence for Meniere’s disease when there is a decreased response to cool and warm stimuli with one ear.
An electrocochleogram (ECoG) is a specialized test which is performed by a qualified audiologist. Electrodes are inserted into the ear canal and around the ear and tones or clicks are used to stimulate the hearing mechanism. The waveform generated from the inner ear (summating potential (SP)) and the waveform generated from the nerve behind the inner ear (action potential (AP)) are compared. With endolymphatic hydrops, the summating potential is enhanced and the action potential is unaffected, thereby enhancing the SP/AP ratio.
An auditory brainstem response and an MRI are tests done to rule out the presence of an acoustic neuroma.
Treatment
Episodic vertigo is the most common reason for patients to seek and pursue treatment.
Dietary Modifications
The initial line of treatment for episodic vertigo is modification of the patient’s diet.
Since it is thought that excessive fluid within the inner ear leads to many of the symptoms, attempts at reducing salt intake can help in reducing the water content of the inner ear. None of us can live without salt in our diet but we can live without fried or preserved foods that are loaded with sodium. Additionally, it is probably wise to avoid adding table salt to your meals.
Caffeine and nicotine can be stimulants to the vestibular system and cause episodes of vertigo. Reducing coffee, tea, chocolate and carbonated soda or switching to decaffeinated versions can be helpful. Reducing or eliminating smoking is not only good for Meniere’s disease but also good for your health in general.
Diuretics
If episodes of vertigo persist despite changes in diet, medication called diuretics can be helpful. These are water pills designed to act on your kidneys to excrete fluid from the body. A common diuretic used in the treatment of Meniere’s disease is a combination of hydrochlorothiazide and triamterene (Dyazide). Triamterene is added to help retain and prevent excessive potassium loss. A common sign of low blood potassium level is cramping pain in the calf. Bananas or dietary potassium supplements can also be taken to offset low potassium levels.
These diuretics are usually used to treat high blood pressure. Consequently these medications can cause low blood pressure. Close monitoring of blood pressure and potassium levels by your primary care physician is recommended.
Other options are available for patients when diet modifications and/or diuretics are either intolerable or fail to control the vertigo spells. These include transtympanic gentamicin, endolymphatic sac surgery, vestibular neurectomy and labyrinthectomy surgery.
Transtympanic Gentamicin
This form of treatment involves the injection of medication through the eardrum into the middle ear. The medication which is then taken up by the inner ear destroys the hair cells of the inner ear. The medication, Gentamicin, is an antibiotic which also is toxic to the hair cells of the hearing and balance organ. The idea is to destroy enough of the hair cells to eliminate the vertigo.
There are advantages and disadvantages of this form of treatment. The attractive feature is that surgery is not required. One of the downsides of this treatment is the potential for hearing loss. Gentamicin is toxic to hair cells of both the hearing and balance organs and once the medicine reaches the middle ear, absorption into the inner ear is uncontrolled and variable. Multiple injections may be required in order to achieve the desired effect.
Endolymphatic Sac Surgery
Another option is a surgical procedure to help drain the endolymphatic sac. Of the surgical options, this is the most conservative operation with minimal risk to hearing. Unfortunately, control of vertigo occurs in only 50-60 percent of patients undergoing this operation. There is no way ahead of time to predict who will or will not respond favorably.
Under general anesthesia, an incision is made behind the ear. The mastoid bone is entered and the endolymphatic sac is decompressed, meaning that the bony covering is removed. The sac is then opened and a shunt tube is inserted. The fluid that would normally enter the sac is shunted away from the inner ear and into the cavity created by the surgery where it is reabsorbed.
This procedure takes about 2 hours to perform and patients can either go home the same day or the next day. The ear may protrude slightly shortly after surgery but should return to its original position in two to three weeks. Numbness around the ear is common and can last for several months.
Vestibular Neurectomy
This is an operation to divide the balance nerves and interrupt the connection between the inner ear and the brain. 90-95 percent of patients who undergo this operation for Meniere’s disease will not have another spell of vertigo. After the operation, dysequilibrium lasts until the brain learns to compensate and adapt to the lack of input from one inner ear. The more patients use their balance system after surgery the less time this adaptation process takes. Anti-dizzy medication such as meclizine and diazepam seem to slow the compensation process.
There are three different approaches or ways to get to the vestibular nerves. The middle fossa approach is the least commonly used and involves an incision above the ear followed by removal of bone over the brain. The roof of the canal through which the balance nerves run is removed and the nerves are then divided. Another approach is the retrolabyrinthine approach which involves incisions behind the ear similar to the endolymphatic shunt procedure. The covering of the brain or dura is opened and spinal fluid is drained. The balance nerves are then divided. A third approach is the suboccipital approach which involves an incision further behind the ear and removal of bone over the covering of the brain. Spinal fluid is drained and the balance nerves visualized and then divided.
The fibers of the hearing and balance nerves run very closely together. Infrequently some hearing loss may occur. Depending on the level of hearing present, the hearing can be monitored during the course of the operation. The facial nerve is the nerve that sends messages to the facial muscles to contract. This nerve lies close to the hearing and balance nerves. Just like hearing, the status of facial nerve functioning can also be monitored. While under general anesthesia recording electrodes are placed in the facial muscles. These electrodes detect contractions of the facial muscles, and the signals are transmitted to a speaker so the surgeon may hear the responses.
Labyrinthectomy
This is an operation to surgically remove a portion of the inner ear. Nearly all patients with Meniere’s disease will be vertigo-free after a labyrinthectomy. Total and complete hearing loss will result in the operated ear. There is no effect on the hearing in the unoperated ear. This is an operation that is recommended to patients that receive no useful hearing in the dysfunctional ear. Just as in vestibular neurectomy, after the operation dysequilibrium lasts until the brain learns to compensate and adapt to the lack of input from one inner ear.
The operation requires general anesthesia and an incision behind the ear. Using a high powered drill the mastoid bone is entered and the semicircular canals are removed.