69 Vestibular Rehabilitation and “PreHab” in Sporadic Vestibular Schwannoma

10.1055/b-0039-169223

69 Vestibular Rehabilitation and “PreHab” in Sporadic Vestibular Schwannoma

Susan J. Herdman and Neil T. Shepard

69.1 Introduction

This chapter provides an overview of vestibular rehabilitation in the context of acute or subacute unilateral vestibular hypofunction, which commonly occurs after vestibular schwannoma (VS) resection. Fundamental principles including theory, exercise strategies, and evidence for treatment efficacy are reviewed. The interested reader is also encouraged to reference Chapter 58 for further discussion regarding the underling pathophysiology, evaluation, management, and outcomes of dizziness in sporadic VS.

The sudden loss of vestibular function caused by the resection of a VS typically causes vertigo, nausea, oscillopsia, dysequilibrium, and unsteadiness of standing balance and gait. Although vertigo, nausea, and the accompanying spontaneous nystagmus usually subside within hours to a few days, imbalance and the sensations of dysequilibrium and oscillopsia, especially during head movement, may endure for many months and can result in extensive time away from work and decreased quality of life.

In recent years, vestibular rehabilitation has been used to help patients make an earlier and more thorough recovery following loss of vestibular function. The use of exercises to improve balance and decrease symptoms specifically in patients with acute loss of vestibular function following VS resection is relatively new. There is, however, clear evidence indicating that vestibular rehabilitation provides substantial benefits to these patients when initiated during the acute or subacute stage following surgery. Following VS surgery, vestibular rehabilitation should be offered to patients who are experiencing symptoms (e.g., dizziness, dysequilibrium, motion sensitivity, oscillopsia) or imbalance due to unilateral vestibular hypofunction during the acute and subacute stage. The goals of early intervention are to (1) decrease the patient’s dysequilibrium (sense of being off-balance); (2) improve the patient’s balance while walking, especially during head movements or turning, thus decreasing the risk for falls; (3) improve the patient’s ability to see clearly during head movements; and (4) enable the patient to resume normal activities more quickly.

The first study to examine whether vestibular rehabilitation would be beneficial for patients following VS resection was published in 1995.s. Literatur The study followed up a group of patients performing simple head movement exercises (see discussion on gaze stabilization exercises later) from postoperative day 3 through postoperative day 6 (day of discharge from the hospital). Balance function and symptom scores of patients performing the exercises were compared to a group of similar patients performing control exercises. The study showed that patients performing the exercises had significantly less dysequilibrium and significant improvement in balance in some posturography measures on the day of discharge. Additionally, more patients in the vestibular exercise group (50%) were able to walk with head turns without staggering than in the control group (0%), suggesting that they would be safer while walking. However, the number of subjects was small (n = 19). Studies that followed this initial paper all found substantial benefits for initiating exercises during the acute stage following VS microsurgery.s. Literatur ^, s. Literatur ^, s. Literatur

69.2 Exercise Approaches

Standard vestibular rehabilitation for the patient with acute vestibular hypofunction typically includes combinations of several different exercises to address the impairments and functional limitations identified during initial evaluation. The goals of the exercises are to (1) foster gaze stability (gaze stability exercises), (2) decrease symptoms (habituation and adaptation exercises), (3) improve standing balance and gait, and (4) improve endurance. Additional treatment approaches that will be discussed include the use of exercise, activity, or chemical ablation of vestibular function prior to surgery (prehab).

Management of patients during the acute stage following resection of VS typically includes medications, such as vestibular suppressants or antiemetics. Several authors have suggested that vestibular suppressant medications such as diazepam may delay or slow recovery by slowing central compensation; however, few studies have examined the influence of medication on the level of recovery when given during the acute stage after surgery.s. Literatur ^, s. Literatur

Patient age should not be considered a deterrent to the use of the exercises. Results from numerous studies have found that age is not a factor in attaining improvement in intensity of subjective complaints, visual acuity during head movement, fall risk, and gait speed in patients performing vestibular exercises.s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur

None of the studies on the use of exercises during the early postoperative stage following VS surgery reported any negative effects; however, the exercises should be used carefully. Although the exercises are performed actively and the patients are advised to make the head movements slowly so that they can see clearly, head movement increases the likelihood of exacerbating dizziness and therefore the exercises should be used only under the supervision of a trained therapist.

69.2.1 Gaze Stability Exercises

Gaze stability exercises were developed based on two concepts. The first concept is that vestibuloocular reflex (VOR) function can be improved through the process of adaptation. Adaptation refers to long-term change in the neuronal response to head movements with the goal of normalizing gaze stability and reducing symptoms. That is, the gain of the VOR can be increased by providing an error signal that the central nervous system then tries to resolve. The primary error signal for VOR adaptation is retinal slip or movement of an image across the retina.s. Literatur To understand this process, it is important to understand that the primary function of the VOR is to keep an image on the fovea of the retina during head movements so that the person can see clearly. If, during head movements, the image moves off the fovea (retinal slip), the image will be blurry. Gaze stability exercises, based on the assumption that they promote vestibular adaptation, involve head movement while maintaining focus on a target, which may be stationary or moving. The goal is for the patient to move his or her head at a velocity that results in a very small amount of visual blurring. The exercises can be modified in numerous ways such as by changing head velocity, distance to the target, duration of maintained head movement, or the visual background against which the exercise is performed. Because the exercises involve head movement, they improve balance as well as gaze stability and symptoms.s. Literatur The second concept underlying the gaze stabilization exercises is based on the principles of substitution. Substitution exercises were developed with the goal of promoting alternative eye movement strategies (e.g., central preprogramming of eye movements, anticipatory saccades) to substitute for lost or reduced vestibular function.s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur For example, in one exercise requiring active eye and head movements between two targets, an eye movement to a target is made before the head movement toward the target; when the head then moves toward the target, the goal is for the patient to keep the eyes on the target. In a healthy individual, the VOR maintains the eyes on the target. In the absence of the VOR, head movements toward the side of a vestibular loss require a different eye movement or eye movements to maintain fixation on the target. Both adaptation and substitution exercises are performed with head movements in the horizontal and vertical planes.

69.2.2 Habituation

Habituation, as a treatment approach, involves repeated exposure to the specific stimulus that provokes dizziness in order to reduce the dizziness. Cawthorne and Cooksey were the first to introduce habituation as an exercise approach in the 1940s.s. Literatur ^, s. Literatur Cawthorne and Cooksey based the exercises on the principle that patients who moved more did better than those who tended to be inactive. These habituation exercises were prescribed for patients with vestibular hypofunction or concussion and involved a progression of activities from eye movements only, head movements with eyes open or closed, bending, tossing a ball, to walking.s. Literatur Patients typically did these exercises in a group. Today habituation exercises are individualized and are chosen based on specific movements (e.g., horizontal head movements) or situations (e.g., busy visual environments) that provoke symptoms.s. Literatur ^, s. Literatur ^, s. Literatur ^, s. Literatur Patients perform several repetitions of body motions, or are exposed to the visual stimulus, that cause mild to moderate symptoms several times a day. This systematic exposure to the provocative stimulus leads to a reduction in symptoms over time. As the patient’s symptoms decrease, the intensity of the exercise can be increased. Other habituation approaches involve the use of optokinetic stimuli or virtual reality environments as habituation exercises.s. Literatur ^, s. Literatur Optokinetic stimuli involves the use of moving visual patterns while virtual reality immerses patients in realistic, visually challenging environments. Both are used to address visual motion sensitivity, also known as visual vertigo, or visually induced dizziness. In both approaches, the stimulus can be graded in intensity by altering stimulus parameters such as velocity of stimulus motion, size of stimulus, and instructions to participant. The stimulus may be provided by optokinetic drums, moving rooms or virtual reality goggles, busy screen savers on a computer, or videos of busy visual environments.