20 Vestibular Rehabilitation

Vestibular disorders can be broadly defined as either stable or unstable lesions. Stable lesions are typically the result of a one-time insult to the system, such as vestibular neuritis or labyrinthitis. Episodic disorders that have been ameliorated through medical or surgical management can also be classified as stable. Examples include patients with Meniere’s disease who have responded to a low-sodium diet and diuresis, ablative therapy through intratympanic gentamicin injection, vestibular nerve sectioning, or labyrinthectomy. Unstable lesions are those that continue to cause episodic bouts of vertigo, dizziness, and disequilibrium, potentially resulting in further degradation of the vestibular system. Examples include unmanaged Meniere’s disease, vestibular migraine, endolymphatic hydrops, and vestibular autoimmune disorders. Although a customized rehabilitation program for patients with Meniere’s disease will have little effect on the episodes associated with unstable lesions, patients may benefit from the secondary hypofunction that develops as the disorder progresses. Residual weakness that results in symptoms of instability, chronic dizziness, and decreased function has been shown to benefit from vestibular rehabilitation.1 Vestibular migraine can also be classified as an unstable lesion due to its episodic and unpredictable nature. Although rehabilitation techniques will not prevent migraine episodes directly, there is evidence that they can significantly reduce symptoms and improve quality of life.^{2,3,4,5,6,7,8} Optimal outcomes are obtained when unstable lesions are stabilized through medical and surgical intervention.

Vestibular disorders can be further classified as unilateral or bilateral, incomplete or complete, symmetric or asymmetric, and peripheral, central, or mixed. Peripheral disorders include any pathology that affects the vestibular end-organs or the vestibular portion of the eighth cranial nerve. An example of a unilateral peripheral dysfunction is vestibular neuritis. Widely studied, patients with peripheral disorders generally compensate within a few weeks if no other limiting factors are present. In patients whose symptoms persist, there is compelling evidence that they improve greatly with a customized rehabilitation program.^{9,10,11,12,13,14,15}

Bilateral peripheral dysfunctions can be seen with ototoxicity from intravenous aminoglycoside administration and with Meniere’s disease. Any of the bilateral peripheral disorders can cause partial or complete loss of function. In the case of complete bilateral loss, patients will experience profound instability, poor gaze stability,16 and be at a higher risk for falls.^17,18,19 Rehabilitation in this population focuses on sensory substitution, facilitating optimization of visual and sensory cues to compensate for the lack of vestibular information. Patient education and functional strategies are an integral part of the program. There is some evidence that patients do improve with a customized program,²⁰ but it is asserted that expectations for complete recovery should be guarded.^17,18,19

Central disorders include any pathology that affects the vestibular nuclei and their myriad connections throughout the brainstem, cerebellum, thalamus, and cortical centers. Recent work with patients recovering from concussion has demonstrated benefit from customized vestibular rehabilitation,^{20,21,22,23,24,25,26,27} as postconcussion dizziness has been a negative predictor of outcome.^28,29 In the case of cerebral vascular accident, dizziness and instability arising from posterior circulation insult were significantly improved following therapeutic modalities, including vestibular rehabilitation techniques,^30,31 but progress is expected to be slower than in patients with peripheral disorders.³² Demyelination at the nerve-root entry zone of cranial nerve VIII occurs in multiple sclerosis and can be classified as a mixed peripheral-central disorder. Other mixed disorders include vestibular schwannomas compromising the cerebellopontine angle, and acquired brain injury with labyrinthine concussion as a sequela.

Classification of vestibular disorders in these categories can assist in prognosis and may determine the most appropriate rehabilitation approach. A combination of vestibular function testing, the bedside clinical exam, performance-based balance measures, and patient reporting will aid in determining the type of vestibular dysfunction that is present.

Disablement Model

The currently accepted model in rehabilitation is the International Classification of Function, Disability, and Health (ICF) developed by the World Health Organization (WHO). This multidirectional interaction model takes into account how the pathologic condition causes impairments in body structure and function and its subsequent impact on an individual’s activity level and participation in activities of daily living. The ICF model is the first to formally acknowledge the influence of personal and environmental factors. The significance of the ICF model lies in its broadened view of how the disease process impacts a person’s ability to function in society.³³ In addition to trying to mitigate the impairments related to the vestibular pathology, all practitioners participating in the care of these individuals need to be mindful of the personal and environmental factors that either help or hinder in the patient’s recovery.

Subjective Questionnaires

No two patients are alike, of course. Even individuals with the same diagnosis will have completely different experiences, time to recovery, and perception of disability. The experience of dizziness and disequilibrium is often difficult for the patient to articulate, much less quantify. To measure the subjective experience and quantify change over time, there are several questionnaires designed specifically for patients with vestibular dysfunction or that have been later validated for this population. Some of the more common questionnaires are listed in Table 20.1.

Objective Testing

Not every patient will arrive for their first therapy session having undergone a complete battery of vestibular function tests, imaging studies, and a complete medical work-up. The number of locales that permit direct access to therapy is growing, and it is incumbent on the treating clinician not only to thoroughly examine the vestibular system (see Chapters 1 and 2 of this book), but also to recognize other red flags that give cause for additional medical assessment. Therefore, it is recommended that every exam include a modified systems review that encompasses the patient’s musculoskeletal system, cardiopulmonary system, and neuromuscular system. A medication review is warranted, because new medications or changes in dosages may contribute to the patient’s symptoms.

Even if the patient has had a complete medical work-up with all possible testing, it is critical that the systems review and bedside examination be repeated, for three reasons. First, there may have been a lapse in time since the patient has seen the referring physician, during which the patient’s medical status has changed. Second, the patient may have experienced additional episodes that have resulted in further insult to the system. As the signs and symptoms pattern has changed, the current working diagnosis may have to be revisited. What was once thought to be a stable process may have been only the first episode in an unstable pathologic process. Finally, the rehabilitation examination of the patient goes beyond diagnosis and prognosis. It is prescriptive. Deficits detected on examination will determine what activities and exercises are used to best facilitate compensation.

Table 20.1 Subjective questionnaires

*ICF, International Classification of Function, Disability, and Health (ICF).

The DGI is an 8-item instrument that assesses the ability to walk with head turns, changes of speed, and negotiation of obstacles. The score for each item ranges from 0 to 3, where 0 is severe impairment and 3 is normal. The highest possible score is 24.41 The ability of the DGI to classify older adults at risk for falls, with scores of < 19/24, has been reported to have a sensitivity of 59% and a specificity of 64%.⁴² Optimal identification of individuals over 60 with balance dysfunction was obtained at a score cutoff point of 22 (sensitivity = 82%, specificity = 88%). The cutoff score for those under 60 was 23 (sensitivity = 96%, specificity = 94%).⁴³

Functional Gait Assessment (FGA)

The FGA is a modification of the DGI that was developed to improve the reliability of the DGI and to reduce the ceiling effect seen with the DGI in patients with vestibular disorders.^44,45 The FGA is a 10-item clinical gait test during which subjects are asked to perform the following gait activities: walk at normal speeds, at fast and slow speeds, with vertical and horizontal head turns, with eyes closed, over obstacles, in tandem, backward, and while negotiating stairs. The FGA is scored on a 4-level (0–3) ordinal scale ranging from 0 to 30, with lower scores indicating greater impairment. The interrater reliability of the FGA in individuals with vestibular disorders was reported as r = 0.86, and the intrarater reliability as r = 0.74. In community-dwelling individuals, the FGA has excellent interrater reliability (ICC = 0.93).⁴⁶

Modified Clinical Test of Sensory Integration and Balance (mCTSIB)

The Clinical Test of Sensory Integration and Balance (CTSIB) closely mirrors the sensory organization test (SOT) component of computerized dynamic posturography (CDP) by evaluating the visual, somatosensory, and vestibular components of balance.⁴⁷ The modified version (mCTSIB) does not use the visual conflict components and tests balance under four conditions: eyes open on firm surface, eyes closed on firm surface, eyes open on foam, and eyes closed on foam (Fig. 20.1).⁴⁸ Scores on mCTSIB have a moderate correlation with the SOT. This correlation is greater when the feet are positioned together than when they are slightly apart.⁴⁹ One of the major benefits to this test is that it requires only a stopwatch and a piece of foam.

Balance Error Scoring System (BESS) Test

The BESS test has been used in several studies for measuring balance deficits connected with sport-related concussion.^50,51 The test utilizes a combination of static balance positions with variations in base of support and surface. Patients are scored by the amount of errors observed in each position. Higher scores represent poorer balance performance. Iverson et al⁵² provided preliminary normative reference values stratified by age groups for the BESS in community-dwelling adults. Psychometric analysis indicated test–retest reliability improved when male (0.92) and female (0.91) participants were evaluated independently.⁵³

Four Square Step Test (FSST)

Originally developed to assess risk for falls in community-dwelling older adults,⁵⁴ the FSST has been validated in patients with vestibular disorders.⁵⁵ Patients are timed as they step clockwise and counterclockwise over four canes arranged in a cross pattern. The FSST has good reliability (ICC = 0.93) and a fall risk cut-off score of 12 seconds (sensitivity = 80%, specificity = 92%).⁵⁶

Concepts of Recovery

There are many terms in the literature used to define recovery following vestibular insult. Terms like compensation, adaptation, habituation, and substitution are used often as distinct entities in the recovery process and in the development of treatment strategies. Compensation can be defined as the functional recovery of the patient, in which the patient has returned to the premorbid activity level with a minimum of symptoms. Adaptation is considered to be a restoration of prior responses at the neurologic level. Habituation is the diminution of a given symptom response by a controlled repeated presentation of a stimulus. Substitution is the utilization of alternate sensations or responses to maintain orientation or perform a given task. Although it does not completely compensate for the vestibular loss, substitution can allow for improved function. Historically, the concepts of recovery have been presented in a hierarchical manner, with substitution at the lowest level, adaptation at its pinnacle, and habituation in between. The reality is that all types of recovery have a role in returning the patient to their prior level of function (Fig. 20.2).

Fig. 20.1 The Modified Clinical Test of Sensory Integration and Balance (mCTSIB). The patient’s static balance is measured under four conditions: (a) Condition 1, Romberg eyes open on a firm surface; (b) Condition 2, Romberg eyes closed on a firm surface; (c) Condition 3, Romberg eyes open on a compliant surface; and (d) Condition 4, Romberg eyes closed on a compliant surface. Assumptions about functional balance under varying sensory cues can be ascertained by comparing scores between conditions. Poorer scores on Condition 2 than on Condition 1 are thought to indicate deficient balance performance with somatosensory cues. Increased difficulty on Condition 3 compared with Condition 1 is indicative of difficulties in using vision to maintain balance. Abnormalities in Condition 4 compared with Condition 3 indicate of deficiency in utilizing vestibular cues in maintaining static balance.

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