Introduction to Meniere's Disease

What is Meniere's Disease?

Meniere's disease is a chronic disorder of the inner ear that while uncomfortable and disruptive to quality of life, is not fatal. All symptoms are related to dysfunction in the organs of the inner ear. According to guidelines of the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS), Meniere's disease is characterized by four symptoms which occur with varying degrees of intensity:

• Vertigo - an intense sense of spinning. This is usually episodic and can range from mild to severe. The vertigo attacks of Meniere's disease are rotational and the duration of each episode must be at least 20 minutes in order to be classified as Meniere's disease.
• Hearing loss - fluctuating low-frequency sensorineural hearing loss that becomes worse during attacks and may permanently deteriorate over time
• Tinnitus - typically a low tone ringing or roaring noise in the ears
• Aural fullness - a sense of fullness in the ear

Vertigo attacks are unpredictable regarding frequency, duration, and severity. They may last from minutes to hours but they don't last more than a day. During an attack, many people lie down with their eyes open until the attack has passed. Meniere's disease impacts strongly on quality of life since the individual may not be able to function with daily tasks. Many individuals alter or limit their daily routine since they don't know when the next attack will occur or how incapacitating it will be.

Initial presentation of symptoms for Meniere's disease is variable among patients. Some people may experience a fully developed attack of Meniere's disease with all of its symptomatic manifestations, while for others, vertigo or other symptoms may appear alone and precede fully developed Meniere's disease by many months or years.

Although the underlying cause of Meniere's is not clear, it has been associated with an excess of endolymph within the cochlear duct and vestibular system. Excess endolymph by itself is known as endolymphatic hydrops and causes symptoms which include hearing loss and tinnitus. When vertigo is present in addition to endolymphatic hydrops, the condition is known as Meniere's disease. There is a subset of people with Meniere's disease who exhibit all of the symptoms but do not have endolymphatic hydrops.

Some of the theories regarding the relationship between endolymphatic hydrops and Meniere's disease include:

• Schuknecht (a noted audiologist) postulated in 1975 that the primary event in the development of endolymphatic hydrops is a viral infection of the inner ear that results in a dysfunction of the control mechanism that balances fluids in the inner ear. The sensory cells of hearing and balance are sensitive to these changes and, subsequently, symptoms of Meniere's develop. This is still a widely accepted theory.
• There is a dysfunction in the production or absorption of endolymph, which allows a buildup of fluid in the ducts. When the hydrops occurs, the pressure causes small ruptures at any point in the membranous labyrinth (Reissner's membrane) and allows the endolymph to mix with perilymph. The mixture of these chemically unique fluids bathes the cochlear and vestibular hairs (nerve receptors) and causes them to stop firing resulting in a temporary loss of function. This sudden change of status causes hearing loss and vestibular imbalance.
• Endolymphatic hydrops causes pressure and mechanical displacement of inner ear organs which then precipitates the attacks.

As a result of the increased pressure in the inner ear and the ensuing distention caused by hydrops, there is irritation of the nerve hairs in the utricle and saccule resulting in additional symptoms of dizziness, imbalance, and disequilibrium. The damage from periodic, intense disturbance to the cochlear duct nerve cells causes hearing loss. Since there is greater pressure at the apex of the cochlea where the nerve cells are sensitive to low frequency sounds, any disturbance affects that area first. For this reason, the first symptoms of hearing loss usually involve low-frequency tones. The fluctuation of endolymphatic pressure is the reason for fluctuation of symptoms in Meniere's disease.

It is not clear if hydrops is a result of obstruction of the endolymphatic duct, overproduction of fluid, or faulty resorption of normal amounts of fluid. It is also not clear whether endolymphatic hydrops is the cause or the result of Meniere's disease since there are cases of endolymphatic hydrops that are asymptomatic.

There is no universally accepted classification system for Meniere's disease. Some researchers describe four different types of Meniere's disease:

• Typical Meniere's disease - patient develops all the symptoms of Meniere's disease
• Atypical Meniere's disease- patient develops either vestibular or hearing symptoms but does not develop full-blown Meniere's disease with all symptoms
• Cochlear Meniere's disease - patient develops fluctuating hearing loss with aural pressure and tinnitus but no vestibular symptoms
• Vestibular Meniere's disease - patient develops episodic vertigo and disequilibrium (loss of equilibrium) without aural symptoms