Your sense of physical balance, or equilibrium, relies on a series of signals that pass from the vestibular organs in the inner ear, through a branch of the 8th cranial nerve (or vestibular nerve), to the brain. The inner ear contains a complex system of fluid-filled chambers and passageways, known as the labyrinth. Changes in body position disturb fluid in the labyrinth and stimulate tiny vestibular hair cells, which then send messages via the vestibular nerve to the cerebellum and brainstem, the balance centers of the brain. This series of cues enables your muscles and eyes to respond almost instantly to changes in position. Abnormalities affecting any part of this system can lead to dizziness, vertigo, and other balance disorders. The following tests may be performed to evaluate balance disorders and determine the origin of the problem:

Electronystagmography (ENG) evaluates nystagmus, or involuntary rapid eye movement, and the muscles that control eye movement. In electronystagmography, electrodes are placed on either side of the eye to provide exact measurements of eye movements at rest, after a change in head position, and in response to various stimuli. Analysis of the pattern of eye movements during this test can help distinguish between abnormalities in the vestibular system, brainstem, and cerebellum.

Posturography (or dynamic platform posturography) is a computerized test that assesses your ability to maintain your standing balance under various conditions. In posturography, you stand on a computer-controlled platform that moves as your body sways. Your responses are recorded and analyzed to diagnose the origin of your balance problem.

The rotary chair test evaluates vestibular and brainstem function. In rotary chair test, you sit in a computer-controlled chair that rotates around a vertical axis. When the chair is rotated in the dark, it induces involuntary rapid eye movement (nystagmus). These movements are recorded, and their speed is compared to the chair rotation at a variety of frequencies to assess vestibular function. The rotary chair test is the most sensitive procedure for detecting loss of vestibular function on both sides (bilateral loss).

Electrocochleography (ECOG) measures electrical activity produced within the cochlea—the primary hearing organ of the inner ear—in response to a sound stimulus. Electrocochleography is used in the diagnosis of Ménière’s disease/endolymphatic hydrops (MD/ELH), a disorder marked by vertigo or severe dizziness, ringing in the ear, fluctuating hearing loss, and pain or pressure in the affected ear.

The caloric study evaluates the function of the vestibular nerve. In the caloric study, cold or hot water is instilled into your ear. This stimulation normally causes characteristic involuntary movements of both eyes (nystagmus). If the labyrinth is diseased, no nystagmus is induced. This test helps to differentiate between vestibular abnormalities and cerebellar or brainstem disorders.

Purpose of Balance Tests

  • To help identify the cause of dizziness, vertigo, or ringing in the ears (tinnitus)
  • To evaluate the function of the vestibular system in the inner ear

Who Performs Balance Tests

  • An ear, nose, and throat specialist (otolaryngologist) or a vestibular technologist
  • A nerve specialist (neurologist) may be involved in the interpretation of the tests.

Special Concerns about Balance Tests

  • ENG and the caloric study should not be performed in people who have a perforated eardrum because of the risk of ear infection.
  • Patients experiencing an acute attack of Ménière’s disease should not undergo the caloric study; the test can be performed once the acute episode subsides.
  • Drugs such as sedatives, stimulants, and antivertigo agents can alter test results.
  • Patients who have pacemakers should not undergo ENG or the rotary chair test because the equipment used in these procedures may interfere with pacemaker function.
  • Because hearing problems may also originate in the middle or inner ear, hearing tests are almost always performed in conjunction with balance tests.

Before Balance Tests

  • Report to your doctor any medications you are taking. You may be advised to discontinue certain drugs before the test.
  • Do not drink caffeine or alcoholic beverages for 24 to 48 hours before balance tests.
  • Avoid eating a heavy meal immediately before testing.
  • If you use a hearing aid or eyeglasses, bring them with you to the testing facility.
  • Women undergoing posturography may want to wear slacks because a safety harness is placed over the clothes during the test.
  • Do not apply any facial makeup before ENG or the rotary chair test because electrodes will be taped to the skin around your eyes.
  • Before ENG, check with your doctor about whether you should stop taking medications, including sedatives and tranquilizers.
  • Prior to ENG and the caloric study, the doctor will examine your ear canal and remove any earwax.
  • Before the caloric study, you will be examined for the presence of nystagmus, Romberg’s sign (a swaying of the body when your feet are placed close together and your eyes are closed), and past-pointing (an inability to accurately touch the examiner’s finger with your index finger when your eyes are either open or closed). This exam will establish certain baseline values for comparison with results obtained during the test.

What You Experience

Electronystagmography (ENG):

  • You will sit or lie down on an examining table in a darkened room.
  • Electrodes are placed above, below and to the side of each eye and attached by adhesive or a band around the head.
  • Different procedures are used to stimulate nystagmus, such as asking you to track a pendulum with your eyes, altering the position of your head or your gaze, and caloric studies.
  • Several recordings of eye movements are made while you are at rest, changing your head or body position, or responding to various procedures (such as having air blown into your ear).
  • The nystagmus response is compared with the expected ranges, and the results are recorded as normal, borderline, or abnormal.
  • This procedure takes about 1 hour.

Posturography:

  • You will stand barefoot on a special computer-controlled platform and try to keep your balance under various conditions.
  • You are surrounded by a 3-sided enclosure with patterns. The enclosure moves as your body moves, and the grade and angle of the platform are changed to provoke balance reactions.
  • Your ability to maintain balance is assessed under increasingly difficult conditions.
  • A computer then isolates each of your sensory inputs and identifies where a balance problem exists.

Rotary chair test:

  • Electrodes are applied to the skin around your eyes.
  • You will sit in a computer-controlled chair that moves very slowly in a full circle. The chair then moves back and forth in a small arc at faster speeds.
  • The testing room is dark, but there will be a video camera focused on your face and a microphone mounted at the top of the chair so you can communicate with the examiner.
  • As the chair turns to the right and left at varying speeds, your eye movements are recorded by the electrodes.

Electrocochleography (ECOG):

  • An electrode is placed inside your ear. In standard ECOG, it is positioned on the eardrum. In transtympanic ECOG, a local anesthetic is used to numb the eardrum and needle electrodes are placed through the drum until they touch the wall of the inner ear.
  • A sound stimulus is applied in the form of clicks and tone bursts of varying frequencies.
  • Recordings are made of the electrical potentials generated in your inner ear in response to the sound stimulation.

Caloric study:

  • Each ear is tested separately. The examiner first places a basin under your ear on the suspected side. Cold water is instilled into your ear canal with a bulb syringe until you complain of nausea and dizziness, or until nystagmus is observed. Nystagmus, which will cause both of your eyes to rapidly turn away from the direction of the cold water and then slowly move back, normally occurs in 20 to 30 seconds.
  • If nystagmus fails to occur after 3 minutes, the irrigation is stopped.
  • The examiner tests you again for nystagmus, Romberg’s sign, and past-pointing.
  • After about 5 minutes, the procedure is repeated on the other side.
  • Sometimes hot water is used in addition to cold water. In such cases, nystagmus should occur in the opposite direction (toward the hot water).
  • The test usually takes about 15 minutes.

Risks and Complications of Balance Tests

  • You may experience nausea, vomiting, and dizziness during all the tests except electrocochleography.
  • Rarely, excessive water pressure during the caloric study can injure a previously damaged eardrum.
  • Transtympanic ECOG has a slight risk of causing otitis media (middle ear infection) or eardrum perforation.

After the Balance Tests

  • If you experienced nausea, vomiting, or dizziness during the test, you will rest in bed for about 30 to 60 minutes until your symptoms subside.
  • Resume your normal diet and any medications withheld before the test, according to your doctor’s instructions.

Balance Test Results

  • A physician will review the test results and consider them along with your symptoms and findings from other tests to reach a diagnosis. Possible causes for balance problems include abnormalities affecting the inner ear, cerebellum, brainstem, and vestibular nerve. Treatment and prognosis depend on the nature of the problem.
  • If your balance tests, symptoms, and physical exam suggest the presence of a growth, the doctor may recommend an imaging test of the head and neck, such as an MRI or a CT scan, to determine the precise type and location of the lesion.

Source:

The Johns Hopkins Consumer Guide to Medical Tests

Simeon Margolis, M.D., Ph.D., Medical Editor

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at Healthcommunities.com

Published: 09 Jan 2012

Last Modified: 09 Jan 2012