David M. Kaylie, MD
Division Otolaryngology - Head and Neck Surgery
Duke University Medical Center
The Vestibular Laboratory was established to provide comprehensive evaluation and management for individuals with chronic vertigo, imbalance, or dizziness. Testing services included in the laboratory evaluation are Electronystagmography (ENG/Caloric Testing), Rotary Chair Testing, and Computerized Dynamic Posturography. Medical-surgical evaluation and management is provided by Drs. Debara Tucci, Joseph Farmer, and John McElveen. In addition to routine evaluation and treatment of the patient with vestibular dysfunction, several rehabilitative programs are available for appropriate candidates.
Vestibular Testing Services
A battery of three vestibular tests are used to assess the physiological and functional status of an individual's vestibular system. The three tests in the battery measure different aspects of peripheral and central vestibular function, and the utilization of this comprehensive testing approach increases the chance of identifying a specific vestibular system problem.
The ENG/Caloric test is the standard for measuring vestibular function. It allows for a bilateral comparison of the vestibular responses induced by bithermal irrigations, as well as measuring spontaneous, gaze, and positional nystagmus. Through computerized recording of the saccadic, smooth pursuit, and optokinetic eye movements, we are also able to assess the integrity of the central structures of the vestibular-oculomotor pathways. While the ENG/Caloric test allows one to identify asymmetry of function between the two sides, the stimulation parameters are such that it mimics only slow head movements. This limits the ENG/Caloric test to assessing one aspect of the vestibular system, and, therefore, some cases of peripheral vestibular dysfunction may be missed by the test.
Rotary Chair Testing
The rotary chair test provides testing of the vestibular system at higher, more natural, frequencies. In this test the individual sits in a chair which is capable of rotating around a vertical axis. When the chair is rotated in the dark, it induces nystagmus. The individual's eye movements are recorded during this rotation, and the velocity of the slow phase of the nystagmus is compared to the chair rotation at a variety of frequencies to derive a measure of the gain, or function of the vestibular system. The gain can be compared to established norms to determine if there is vestibular hypofunction or hyperfunction. When tested at higher velocities of rotation, it is possible to determine a measure of asymmetry (or unilateral weakness). In addition to these measures of vestibular system gain, the rotary chair test also allows one to determine the duration of the vestibular response through measures of the time constant. The interaction of the gain and time constant measures are useful in determining whether the vestibular loss is an acute or chronic condition. A prolonged vestibular response may also be found in individuals who suffer from motion sickness. This finding in this particular population can be used to design a treatment program to alleviate the motion sickness. The rotary chair test is also the most useful method to document bilateral vestibular loss.
Computerized dynamic posturography is a test of the vestibulospinal system and assesses an individual's ability to maintain standing balance under a variety of sensory conditions. During the posturography test, the individual stands on two force plates which measure the individual's postural sway. The dynamic posturography test actually consists of several different subsets of tests. The sensory organization subtests document performance on six conditions that quantify the patient's ability to use visual, somatosensory, and vestibular cues to maintain standing balance. The motor coordination subtests measure the automatic postural reactions to sudden translational or pitch movements of the support surface. The third subtest, the EMG test, measures the integrity of peripheral and central pathways for motor innervation of the lower limbs as reflected by the onset of motor responses to rotational movements of the support surface. Responses are measured by surface electrode electromyography (EMG), and related to normal values by age. While the posturography test is a non-localizing test, patterns of performance on the various subtests arehelpful in diagnosis of the etiology of vestibular dysfunction. specific patterns of performance on the sensory organization subtests are characteristic of individuals with peripheral vestibular dysfunction. The results of the sensory organization test can also be used to design appropriate treatment programs and quantitatively document changes in postural stability over the course of therapy. In addition, the sensory organization component of the test can be used to identify "non-physiologic" or functional balance problems. Abnormal findings in the motor control tests or EMG test are indicative of central rather than peripheral vestibular problems.
Medical/ Surgical Evaluation and Management
When desired by the referring physician, patients may also be scheduled for a neurotologic evaluation by staff otologists experienced in the diagnosis and medical and surgical management of patients with vestibular disorders. This evaluation is not automatic with referral to the Vestibular Laboratory, and should be scheduled separately with the appointment secretary.
Vestibular Rehabilitation Evaluation and Management
Approximately 15 out of 1000 individuals consult their family physicians each year with complaints of vertigo, dizziness, or imbalance; in addition half of the individuals over the age of 65 will develop positional vertigo. Many of these individuals will have vestibular problems which are not amenable to surgical treatment, and pharmacological treatment of these conditions with vestibular suppressants often retards the recovery process. Those individuals who undergo surgical treatment may be left with a chronic unilateral vestibular loss. While some of the individuals in each of these groups will experience resolution of their symptoms due to central nervous system ccompensation, others will be left with chronic dizziness or imabalance. Recent studies have shown that these patients often benefit from vestibular rehabilitation exercises designed to enhance the central nervous system's adaptation process, increase the individual's postural stability, or relieve the specific symptoms.
Vestibular rehabilitation services provided through the Vestibular Laboratory focus on evaluation of the patient's functional abilities and assessment of positions or movements that provoke the patient's symptoms. Based on these findings, an appropriate therapy program is designed to minimize those symptoms, improve the patient's balance, and increase their functional status. Patients are initially treated, given a customized exercise program to be conducted at home when necessary, and then followed at appropriate intervals.
Patients can be referred to the Vestibular Laboratory for vestibular testing with or without medical evaluation or vestibular rehabilitation. Appropriate referrals are for patients with a history of chronic dizziness or imbalance lasting six weeks or longer. We recommend that patients with chronic dizziness who have not had a complete evaluation be referred for vestibular testing and medical evaluation. Referral for vestibular rehabilitation will be made if indicated. Individuals who have had a complete medical otologic evaluation can be referred specifically for further vestibular testing and vestibular rehabilitation. Patients who demonstrate evidence of central vestibular pathology can be referred to a neurologist experienced in the evaluation of these disorders, if requested by the referring physician.