VESTIBULAR DISORDERS

Vestibular Assessment and Rehabilitation

With more than half the US population affected by balance or vestibular disorders at some point in their lives¹, the need for effective diagnostic and treatment approaches is clear. Unfortunately, diagnosis and treatment of balance disorders that do not quickly resolve on their own has historically been difficult due to the complex, multifactoral nature of the problems.

Balance control is a complex process that depends on appropriate organization of information from the gaze stabilization and postural stabilization systems, and coordinated responses of the voluntary and automatic motor systems. Dizziness and imbalance can be caused by disruptions in any one of these systems, or in the adaptive brain mechanisms that coordinate the actions of these systems.

Vestibular system integrity is important in the balance control process, but it is only one factor in the evaluation of balance function. Even when specific vestibular pathology is identified, the diagnostic and treatment planning process is incomplete, as the patient’s status may be further complicated by problems in other sensory or motor systems, or problems in the brain’s adaptive functions. "The first task of the practitioner, therefore, is to determine whether the problem is sensory, integrative, or motor in nature" (Goebel).² Once this has been established, then an effective treatment plan can be prescribed, including medical, surgical, or rehabilitative strategies as appropriate.

The Complete Balance Assessment

The patient with chronic dizziness, unsteadiness or imbalance is best served by starting with a comprehensive clinical evaluation, which includes

History, focusing on both the nature of the dizziness and the associated symptoms
Physical examination, including oculomotor and vestibuloocular reflexes (VOR), positioning tests, and evaluation of cerebellar, posture and gait functions

Objective tests are then used to confirm or refute a diagnostic hypothoses formulated during the clinical evaluation, and to identify the functional impairments resulting from the disease.

Site-of-lesion testing, such as ENG, Rotary Chair, MRI
Sensory, motor, and brain adaptive impairment testing, such as CDP

Effective treatment planning takes into consideration both pathology and underlying impairments, and target those specific components of the balance disorder. Controlled outcome studies have demonstrated that outcomes improves significantly when rehabilitation is customized to target specific impairments.^{3,
4} Further, objective measures of balance impairment establish a baseline to evaluate and document progress through rehabilitation.

For the complex balance patient, traditional diagnostic tests (ENG, rotary chair, MRI, etc.), are helpful in confirming site-of-lesion diagnoses, but they do not isolate the patient's functional problems. Objective measures of underlying sensory/motor/adaptive impairments provide complementary functional information that is essential for effective treatment planning and outcome documentation.

Advances in computerized assessment technology have made it possible to isolate and quantify specific impairments related to vestibular, somatosensory, and visual inputs to balance; automatic motor responses and movement strategies; voluntary motor responses; center of gravity alignment and weight bearing; and planning and coordination of weight transfers for mobility function. Medical devices are available that aid the clinician in classifying patients in terms of specific pathology and specific impairments, as well as the resulting functional limitations. This comprehensive information enables the effective integration of traditional surgical and medical treatment options with targeted rehabilitation methods. This evidence based approach allows the clinician to minimize the impact of pathology and maximize the patient's functional performance abilities.

Tests of Vestibular and Balance Function

A review of the information provided by the routine vestibular and balance studies illustrates how site-of-lesion and impairment tests may be utilized in a collective manner to assist in patient management and which tests would be the most useful and appropriate for a given patient.^{5, 6, 7, 8}

Extent & Site of Lesion:

Electronystagmography (ENG) – electrodes or video
Rotational Chair
Motor components of Computerized Dynamic Posturography (CDP)
Vestibular Evoked Myogenic Potentials
Audiometric Tests
Imaging Tests
Serologic Studies

Impairments/Functional Performance/Objectify Complaints:

The preceding list highlights the designed utility of the available clinical tests. It does not, however, reflect the way they are utilized. Typically, it is the combination of test findings that are used to develop a final impression from the evaluation.⁹ The site-of-lesion tests are typically used to confirm the presumptive diagnosis, although there are situations where unexpected results alter the initial presumption.⁹ The site-of-lesion and impairment tests are then used to identify those underlying problems having the greatest impact on the patient’s symptoms and functional limitations, and those most likely to respond positively to treatment.

Vestibular and Balance Rehab

Vestibular and balance rehabilitation is effective for appropriately identified patients and when customized to target specific impairment problems. The comprehensive balance assessment, which includes pathology, underlying impairments and functional limitations, can provide the necessary data for accurate treatment customization. The rehabilitation intervention itself is most appropriately provided by specially trained rehabilitation professionals familiar with the appropriate sensory, motor and adaptive training exercises.

Specifically, the specialist providing the rehabilitation component of the program should possess advanced training in the area of vestibular dysfunction and balance. Currently, core physical therapy education does not include entry-level knowledge of this complex patient population. For vestibular rehabilitation and balance retraining therapy, the hallmarks to look for in a rehabilitation professional is a thorough understanding of the interactions among pathological and impairment mechanisms and the use of objective assessment data for treatment planning that targets the individual patient’s specific needs.

To maximize the benefit of a rehabilitation program, the prescribed exercises must focus on resolving the underlying impairments and functional limitations. The exercises must also be appropriately challenging and keep the patient motivated. A generic approach to balance treatment will not be as effective as an approach that singles out the underlying impairments, and may not improve function at all.

To support effective treatment planning and improve functional outcomes, the clinician may use computerized training protocols, which can be customized to target the specific impairments of the individual patient. Deficits in multi-sensory integration exist in many individuals with vestibular loss. Retraining should, therefore, include protocols to address the sensory processing deficits, including sensory substitution and sensory-challenge exercises. Further, prescribed tasks in a variety of environments (unstable surface, moving visual field) will require the patient to update and prioritize sensory inputs and motor response. The difficulty level of the targeted exercises can be adjusted to match patient ability, and then increased to keep the patient challenged and maximize learning as the patient recovers.

Real time visual biofeedback further enhances motor learning by helping the patient understand the prescribed training task, and by providing both the patient and the clinician with instant feedback on how they are performing a prescribed task. As treatment progresses, this feedback can be gradually withdrawn and then eliminated as the patient’s functional capabilities improve and newly learned skills are integrated into more complex motor activities.

Summary

By accurately identifying pathology, as well as underlying sensory/motor/central adaptive impairments and functional limitations, patient care and functional outcome can be significantly improved. To aid in accurate diagnosis and objective functional assessment, the physician should follow a systematic and standardized procedure for each patient, beginning with a thorough history and physical exam. Based on the findings of this initial evaluation a presumptive or conclusive diagnosis may be made in some instances. When the diagnosis is presumptive, site of lesion testing such as ENG, rotary chair may be warranted. Whether or not a conclusive diagnosis can be established, treatments can only be effectively targeted after the patient's underlying impairments and functional limitations have been quantified.

References:

National Institute on Deafness and Other Communication Disorders, March 1997
Goebel, JA (ed.) (2001) Practical Management of the Dizzy Patient. Lippincott, Williams & Wilkins.
Black F, Angel C, Pesznecker S, Gianna C. "Outcome analysis of individualized vestibular rehabilitation protocols." Am J Otology 2000 21:543-551.
Rose D, Clark S (2000). "Can the control of bodily orientation be significantly improved in a group of older adults with a history of falls?" JAGS 48:275-282.
Baloh RW, Halmagyi GM (eds.) (1996). Disorders of the vestibular system. New York: Oxford University Press.
Leigh RJ, Zee DS (1999). The Neurology of Eye Movements. 3rd ed. Philadelphia: F.A. Davis Company.
Halmagyi GM & Colebatch JG (1995). "Vestibular evoked myogenic potentials in the sternoclidomastoid muscle are not of lateral canal origin." Acta Otolaryngol (Stockh) supp 520, pp 1-3.
Shepard NT & Howarth AE (1999). Vestibulocollic auditory evoked potentials: Normative ranges. Midwinter Research Meeting of the ARO.
Shepard NT (2003). Laboratory Studies in the Management of the Dizzy and Balance Disordered Patient. NeuroCom Short Communication Publication. NeuroCom International, Inc., Clackamas, OR.