Balance Disorders

A balance disorder is a disturbance that causes an individual to feel unsteady, giddy, woozy, or have a sensation of movement, spinning, or floating. An organ in our inner ear, the labyrinth, is an important part of our vestibular (balance) system. The labyrinth interacts with other systems in the body, such as the visual (eyes) and skeletal (bones and joints) systems, to maintain the body's position. These systems, along with the brain and the nervous system, can be the source of balance problems.

An integral part of the labyrinth is the system of semicircular canals. These canals let us know when we are in a rotary (circular) motion. The semicircular canals comprise fluid-filled superior, posterior, and horizontal canals. Motion of the fluid tells us if we are moving. The semicircular canals and the visual and skeletal systems have specific functions that determine an individual's orientation in space. The vestibule is the region of the inner ear where the semicircular canals come together, close to the cochlea (the hearing organ). The vestibular system works with the visual system to keep objects in focus when the head is moving. The brain receives, interprets, and processes the information from these systems, along with signals from joint and muscle receptors, to control balance.

Illustration of the labyrinth's structures: the semicircular canals, the vestibule and the cochlea. Source: NIDCD, NIH

Normal Function of the Vestibular System

Movement of fluid in the semicircular canals detects the direction and speed of rotation of the head–for example, whether we are nodding our head up and down or looking from right to left. Each semicircular canal has a bulbed end, or enlarged portion, that contains hair cells. Rotation of the head causes a flow of fluid, which in turn causes displacement of the top portion of the hair cells that are embedded in the jelly-like cupula. Two other organs that are part of the vestibular system are the utricle and saccule. These are called the otolithic organs and are responsible for detecting linear acceleration (movement in a straight line). The hair cells of the otolithic organs are blanketed with a jelly-like layer studded with tiny calcium stones called otoconia. When the head is tilted or the body position is changed with respect to gravity, the displacement of the stones causes the hair cells to bend.

Illustration of the flow of fluid in the ear, which in turn causes displacement of the top portion of the hair cells that are embedded in the jelly-like cupula. Also shows the utricle and saccule-otolithic organs that are responsible for detecting linear acceleration, or movement in a straight line. Source: NIDCD, NIH

This figure shows nerve activity associated with rotational-induced physiologic nystagmus and spontaneous nystagmus resulting from a lesion of one labyrinth. Thin straight arrows--direction of slow components; thick straight arrows--direction of fast components; curved arrows--direction of flow in the horizontal semicircular canals: AC--anterior canal, PC--posterior canal, HC--horizontal canal. Source: NIDCD, NIH

Types

Below are some of the more common balance disorders:

Benign Paroxysmal Positional Vertigo (BPPV)–a brief, intense sensation of vertigo that occurs because of a specific positional change of the head. An individual may experience BPPV when rolling over to the left or right upon getting out of bed in the morning, or when looking up for an object on a high shelf. Inner ear infection, head injury, or aging are thought to cause BPPV.

Labyrinthitis–an infection or inflammation of the inner ear causing dizziness and loss of balance.

Ménière's disease–a balance disorder involving the fluid of the inner ear. This disorder causes episodes of vertigo, fluctuating hearing loss, tinnitus (a ringing or roaring in the ears), and the sensation of fullness in the ear. The cause of Ménière's disease is unknown.

Vestibular neuronitis–an infection, usually viral, of the vestibular nerve.

Perilymph fistula–a leakage of inner ear fluid into the middle ear. This problem can occur after head injury, physical exertion or, rarely, without a known cause.

Signs and Symptoms

When balance is impaired, an individual has difficulty maintaining orientation. For example, an individual may experience the "room spinning" and may not be able to walk without staggering, or may not even be able to arise. Balance disorders have several symptoms:

• A sensation of dizziness or vertigo (spinning)
• Falling or having a sensation of falling
• Lightheadedness or feeling woozy
• Visual blurring
• Disorientation

Some individuals may also experience nausea and vomiting, diarrhea, faintness, changes in heart rate and blood pressure, fear, anxiety, or panic. Some reactions to the symptoms are fatigue, depression, and decreased concentration. The symptoms may appear and disappear over short time periods or may last for a long period of time.

Causes

Infections (viral or bacterial), head injury, disorders of blood circulation affecting the inner ear or brain, certain medications, and aging may change the balance system and result in a balance problem. Individuals who have illnesses, brain disorders, or injuries of the visual or skeletal systems, such as eye muscle imbalance and arthritis, may also experience balance difficulties. A conflict of signals to the brain about the sensation of movement can cause motion sickness (for instance, when an individual tries to read while riding in a car). Balance disorders can be due to problems in any of four areas:

• Peripheral vestibular disorder, a disturbance in the labyrinth.
• Central vestibular disorder, a problem in the brain or its connecting nerves.
• Systemic disorder, a problem of the body other than the head and brain.
• Vascular disorder, or blood flow problems.

Diagnosis

Diagnosis is complicated by the various causes of balance disorders, including those associated with other conditions such as ear infections, blood pressure changes, and some vision problems.

Often balance disorders are diagnosed with the aid of an otolaryngologist. An otolaryngologist is a physician/surgeon who specializes in diseases and disorders of the ear, nose, throat, head, and neck. Many otolaryngolosists have special expertise in balance disorders. Possible causes of the disorder are evaluated using detailed medical histories and physical examinations. The physician may require tests to assess the cause and extent of the disruption of balance. The kinds of tests needed vary depending on symptoms and health status. Because there are so many variables, not every test is needed in every patient.

Some examples of diagnostic tests include hearing examinations, blood tests, an electronystagmogram (ENG–a test of the vestibular system), or imaging studies of the head and brain.

A caloric test is sometimes performed as part of the ENG. In this test, nystagmus is determined by flushing each ear with warm, then cool, water. Weak or absent nystagmus may indicate an inner ear disorder.

Another test of the vestibular system, posturography, requires the individual to stand on a special platform capable of movement within a controlled visual environment. Body sway is recorded in response to movement of the platform and/or the visual environment.

Treatment

There are various options for treating balance disorders. One option includes treatment for a disease or disorder that may be contributing to the balance problem. Treatment varies and is based on symptoms, medical history, general health, examination by a physician, and the results of medical tests.

One treatment option includes balance retraining exercises (vestibular rehabilitation). These exercises include movements of the head and body specifically developed for the affected person. This form of therapy is thought to help compensate for some of the symptoms of the disorder.

Several other treatment options are available. For people diagnosed with Ménière's disease, reduced sodium intake and other dietary changes are sometimes helpful. Reductions in Alcohol and caffeine consumption, as well as in nicotine use, also help some people. People with anxiety may respond to programs of talk therapy and/or physical rehabilitation. Some aminoglycoside antibiotics, such as gentamicin (Gentak) and streptomycin, are used to treat Ménière's disease. Systemic streptomycin (given by injection) and topical gentamicin (given directly to the inner ear) are useful because they directly influence the motion of hair cells. However, Gentamicin can also affect the hair cells of the cochlea and cause hearing loss. Balance disorders that do not respond to any of these treatments may require surgery.

Research

Research on balance disorders is proceeding on several fronts:

• understanding of the various balance disorders and the complex interactions between the labyrinth, other balance-sensing organs, and the brain
• study of eye movements to understand the changes that occur in aging, disease, and injury
• study of posture and eye movements to improve diagnosis and treatment
• study of the effectiveness of certain exercises as a treatment option

Research in chinchillas has yielded a potential new therapeutic approach. In one study, chinchillas were treated with gentamycin to impair the vestibular system and mimic a balance disorder.^[1] Battery-operated multichannel vestibular prosthesis were then placed on the chinchillas’ heads. The prosthesis is designed to place sensors outside the head and parallel to the semicircular canals. The sensors send movement information to electrodes implanted in the inner ear, essentially replacing the information that would normally be sent by the semicircular canals. Much more work is needed before the technology is adapted for use in humans.

Recent findings from studies supported by the National Institute on Deafness and Other Communication Disorders (NIDCD) suggest that the vestibular system plays an important role in modulating blood pressure. The information from these studies has potential clinical relevance in understanding and managing orthostatic hypotension (lowered blood pressure related to a change in body posture). Other studies of the otolithic organs, the detectors of linear movement, are exploring how these organs differentiate between downward (gravitational) motion from linear (forward-to-aft, side-to-side) motion.

Other projects supported by NIDCD include studies of the genes essential to normal development and function in the vestibular system. Scientists are also studying inherited syndromes of the brain that affect balance and coordination.

The Institute supports research to develop new tests and refine current tests of balance and vestibular function. For example, scientists have developed computer-controlled systems to measure eye movement and body position by stimulating specific parts of the vestibular and nervous systems. Other tests to determine disability, as well as new physical rehabilitation strategies, are under investigation in clinical and research settings.

NIDCD, along with other Institutes at the National Institutes of Health, joined the National Aeronautics and Space Administration (NASA) for Neurolab, a research mission dedicated to the study of life sciences. Neurolab focused on the most complex and least understood part of the human body, the nervous system (including the balance system).

Exposure to the weightlessness of space is known to temporarily disrupt balance on return to Earth and to gravity. A team of NIDCD and NASA investigators had previously studied the effects of microgravity exposure on balance control in astronauts who had returned from short-duration space flight missions, but these studies did not include an aged individual. During the October 29-November 7, 1998, Space Shuttle Discovery mission, NIDCD and NASA collaborated in another study of postflight balance control. For the first time, a previously experienced, but now elderly astronaut, Senator John Glenn, participated. Data collected during this mission, which are still being analyzed, may help to explain the mechanisms of recovery from balance disorders experienced on Earth as well as in the space environment. Scientists also hope that this data will help to develop strategies to prevent injury from falls, a common occurrence among people with balance disorders, particularly as they grow older.

Epidemiology

Estimates suggest that the incidence of dizziness, imbalance, and vertigo are 5%–10% and as high as 40% in people over the age of 40 years. dizziness, vertigo, and imbalance is 5-10%, and it reaches 40% in patients older than 40 years. ^[2]

References

1. ↑ Della Santina CC, Migliaccio AA, Patel AH. A multichannel semicircular canal neural prosthesis using electrical stimulation to restore 3-d vestibular sensation. IEEE Trans Biomed Eng. 2007 Jun;54(6 Pt 1):1016-30. Abstract Press Release
2. ↑ Friedman M. eMedicine Web site. Dizziness, Vertigo, and Imbalance

External Links

Vestibular Disorders Association