Chapter 13 Vestibular rehabilitation

Introduction 267

Incidence and prevalence of dizziness and balance disorders 268

Normal anatomy and physiology 268

Peripheral vestibular system 268

Central vestibular system 269

Vestibulo-ocular reflex and vestibulospinal reflex 269

Evidence base for vestibular rehabilitation 284

Specialist centres and support groups 284

Conclusion 284

Case histories 284

The overwhelming vertigo, the awful sickness and the turbulent eye movements – all enhanced by the slightest movement of the head, combine to form a picture of helpless misery that has few parallels in the whole field of injury and disease.

Cawthorne, 1945

Introduction

Normal postural control, or ‘balance’ as it is commonly known, is fundamental to activities of daily living. Visual, vestibular and somatosensory systems all have important and integrated roles to play in the maintenance of balance and the neurological patient can present with problems in any or all of these components.

This chapter will focus on the assessment and treatment of patients who have a primary problem in the vestibular system. Vestibular dysfunction is characterized by a number of signs and symptoms, including vertigo, gait and balance impairment, nausea and nystagmus (Table 13.1).

Table 13.1 Signs and symptoms of vestibular disorders

Primary symptoms and signs	Associated problems
Vertigo	Neck and back pain
Dizziness/light-headedness	Physical deconditioning
Nausea and vomiting	Agoraphobia
Oscillopsia	Hyperventilation
Nystagmus	Falls
Disequilibrium/impaired balance	Hearing loss/tinnitus
Panic/anxiety
Gait abnormality
Fatigue

Patients with such dysfunction present the physiotherapist with specific problems and require specialized assessment and treatment techniques, collectively referred to as vestibular rehabilitation. Vestibular rehabilitation has its roots in the empirical work of Cawthorne and Cooksey who, in the 1940s, first documented the important role of exercise in recovery after a vestibular injury (Cooksey, 1945).

There is now a moderately strong evidence base to support the role of physiotherapy in the management of patients with vestibular disorders (Hillier & Holohan, 2007; Hilton & Pinder, 2004) and vestibular rehabilitation is recognized as a specialist area within physiotherapy.

Key point

Vertigo is defined as the sensation of motion when no motion is occurring relative to the Earth’s gravity (Monsell et al., 1997). The sensation can be of the patient moving in relation to the environment or the environment moving in relation to the patient. It is generally accepted that true vertigo involves a spinning sensation and usually indicates inner-ear pathology (Blakley & Goebel, 2001). The word ‘dizziness’ is used to describe non-rotatory vertigo. These definitions should be considered when taking the patient’s history as they will give clues to the underlying pathology.

Incidence and prevalence of dizziness and balance disorders

The prevalence of dizziness has been estimated to be one in five in the 18–64 age group with 50% of these reporting postural unsteadiness (Yardley et al., 1998b). Prevalence rises to one in three in the over-65s (Colledge et al., 1994) and dizziness is the most common complaint of patients presenting to primary care in those aged over 75 (Sloane, 1989). However, approximately 40% of patients with a complaint of dizziness do not consult their general practitioner, demonstrating a probable underestimation of the problem (Yardley et al., 1998b). There is a very low prevalence of dizziness in the under-25s and women are more likely to experience dizziness. Dizziness rarely results in hospitalization and the majority of patients are managed at primary care level with medication (Sloane, 1989).

Normal anatomy and physiology

The anatomy and physiology of the vestibular system are extremely complex and the reader is referred to Cohen (1999) and (Schubert & Minor, 2004) for a detailed description. A brief organizational overview is shown in Figure 13.1. The vestibular system has both sensory and motor functions and is generally divided into peripheral and central components. The peripheral system consists of the vestibular end organ and the vestibular nerve up to and including the dorsal root entry zone. The central system includes the vestibular nuclei in the brainstem and their central connections.

Figure 13.1 Functional organization of the vestibular system and vestibular labyrinth (top right).

Peripheral vestibular system

The vestibular end organ includes the semicircular canals (SCC) and the otoliths (utricle and saccule). There are three SCCs on each side (horizontal, anterior and posterior) and they are oriented at approximately 90° angles to each other (Figure 13.1). Each canal is coupled functionally with a canal in the opposite end organ, i.e. both horizontal canals are coupled, as are the left anterior and right posterior, and the right posterior and left anterior canals. Specialized sensors known as hair cells are located in the semicircular canals in a region known as the cupula (Figure 13.1) and respond to angular velocity of head movement in different planes. Each canal responds best to movement in its own plane. For example, if the head turns to the right, the hair cells in the right horizontal SCC increase their firing rate and those in the left horizontal SCC decrease their firing rate (Figure 13.2). Thus the central nervous system (CNS) gains information relating to the velocity and direction of head movement.

Figure 13.2 Function of the horizontal canals in generating a vestibulo-ocular reflex (VOR) during turning of the head and effect of loss of hair cell function. With loss of tonic firing on the right there is a relative increase in firing on the left; the brain interprets this as movement to the left (patient feels dizzy) and generates a VOR so that the eyes move to the right. The central nervous system corrects the eye movement with a saccadic movement to left, and a left-beating nystagmus is seen. (Firing rate for illustrative purposes only.)

The otoliths have different hair cells in a region known as the macula, and these are covered by a layer of calcium carbonate crystals called otoconia. They respond to the force of gravity and thus can provide the CNS with information on head tilt and linear acceleration (i.e. going up and down in a lift or going forwards or backwards in a car).

The peripheral system is a tonically active system, i.e. it always has a certain firing level (about 70–100 spikes per second), which will increase or decrease with head movement. The CNS interprets any asymmetry in the firing rate as movement. This fact is of utmost importance when considering a patient who has loss of vestibular function on one side (i.e. decrease or absence of firing) since there will be a relative increase of firing on the intact side even when the head is not moving (Figure 13.2). This asymmetry and the resultant disturbance in cortical spatial orientation are thought to form the basis of vertigo (Brandt, 2000a). Afferent nerve fibres arising from hair cells collect to form the vestibular nerve, which enters the brain at the pontomedullary junction.

Central vestibular system

The vestibular nerve sends fibres to two main areas: the vestibular nuclei (in the pons and the medulla) and the cerebellum (Figure 13.1). The vestibular nuclei are responsible for integrating information received from the vestibular end organ with that received from other sensory systems and the cerebellum. Vestibular nuclei send fibres to the oculomotor nuclei, vestibulospinal tracts, contralateral vestibular nuclei, reticular formation, thalamus, cerebellum, autonomic nervous system and the cortex. The parietal and insular areas of the cortex appear to be a specialized vestibular area (Brandt et al., 2002). The symptoms of nausea, vomiting and anxiety associated with vestibular disorders are thought to be a result of abnormal activation of the autonomic and reticular pathways respectively (Figure 13.1).

Vestibulo-ocular reflex and vestibulospinal reflex

The motor functions of the vestibular system include the vestibulo-ocular reflex (VOR) and the vestibulospinal reflex (VSR). The function of the VOR is to maintain stable vision when the head is moving. A good example of this is being able to focus on an object when walking. If the eyes moved with the head as it goes up and down when walking it would be impossible to see clearly. The VOR enables the eyes (through activation of the appropriate ocular muscles) to move in the opposite direction and at an equal velocity to the head. The image of the object thus remains stable on the retina. For the VOR to function normally, the velocity of eye movement must be equal to and in the opposite direction from the head movement. This is known as the ‘gain’ of the VOR. Patients who have problems with the vestibular system have impairment of the gain of the VOR and therefore demonstrate problems with gaze stability. They often describe that during self-motion stationary objects seem as if they are moving. The function of the VSR is primarily to maintain and regain postural control and this is achieved through activation of monosynaptic and polysynaptic vestibulospinal pathways.

Classification and causes of vestibular disorders

Vestibular disorders are classified anatomically into peripheral or central, depending on which area the pathology affects. Common peripheral and central vestibular disorders are shown in Table 13.2. It is important to note that dizziness is not always caused by pathology affecting the vestibular system; there may be many other causes, including postural hypotension, cardiac disorders, psychiatric disorders and hyperventilation, and these should be evaluated prior to referral to physiotherapy. The exact cause of dizziness frequently remains uncertain and a trial of vestibular rehabilitation may be suggested in the absence of a specific diagnosis. The pathologies of disorders that can affect the central vestibular system (particularly cerebrovascular accidents, traumatic brain injury and multiple sclerosis) are considered in other chapters.

Table 13.2 Peripheral and central vestibular disorders

Peripheral	Central
Viral – vestibular neuritis/labyrinthitis	Ischaemia, e.g. lateral medullary syndrome (Wallenburg’s syndrome)
Benign paroxysmal positional vertigo (BPPV)
Perilymph fistula	Vertebrobasilar insufficiency
Ménière’s disease	Infection
Vascular occlusion	Head injury
Iatrogenic (ototoxic drugs, surgery)	Degenerative disease, e.g. multiple sclerosis
Head injury	Friedreich’s ataxia
Acoustic neuromas (may have a central component)	Base-of-skull abnormalities, e.g. Arnold–Chiari malformation
	Tumours of the cerebellopontine angle
	Drugs
	Epilepsy
	Migraine

Peripheral disorders

Vestibular neuritis

This condition is also called neuronitis and is a common peripheral vestibular problem thought to be caused by a virus. It results in hair cell loss and unilateral vestibular paresis (or hypofunction). Patients present with an acute onset of vertigo, nausea and vomiting that is severely incapacitating and worsened by head and eye movements. On examination a spontaneous horizontal nystagmus can be seen, the fast phase of which beats away from the involved side. This is due to the asymmetrical tonic firing of the vestibular nerves (Figure 13.2). Balance and gait abnormalities are also evident. Hearing is not generally affected; if it is, the condition is called labyrinthitis. These symptoms generally resolve over a period of 2–6 weeks.

Benign paroxysmal positional vertigo

Benign paroxysmal positional vertigo (BPPV) is the commonest cause of vertigo in peripheral vestibular disorders. It has a lifetime prevalence of 2.4% (Marom et al., 2009) and is more common in females (Baloh et al., 1987). Its aetiology is unknown in many cases but it can occur as a result of an earlier vestibular neuritis or head trauma. The name encompasses the following associated features:

• Benign – the prognosis for recovery is favourable

• Paroxysmal – the associated vertigo is short-lived, generally less than 1 minute

• Positional – the vertigo is provoked by head positioning

• Vertigo – a spinning sensation is experienced.

BPPV is thought to be caused by detached utricular otoconia entering one of the SCCs and either floating free in the canal (canalithiasis) or adhering to the cupula (cupulolithiasis; Epley, 1980). This has the effect of making the SCC with the displaced otoconia in it responsive to gravity when normally it is not. The SCCs usually respond to head movement in their respective planes and increase or decrease their firing rate during head movement, returning to normal tonic firing level when the head has stopped moving. However, the displaced otoconia are heavier, continue to move in the canal and stimulate the hair cells in the canal to continue firing. The central vestibular system interprets this as further movement and generates a VOR for that canal, and the patient develops nystagmus and vertigo.

This nystagmus, following movement into the provoking position, has a latency of 1–50 seconds, is generally transient in nature (it stops when the otoconia come to a resting position) and is most commonly torsional towards the affected ear. If the patient repeatedly moves into the provoking position the vertigo and nystagmus will decrease due to habituation of the response (Baloh et al., 1987).

The diagnosis of BPPV is generally made using the Hallpike–Dix manoeuvre (Figure 13.3, Table 13.3) in which the head is moved into a provocative position. BPPV is most commonly caused by canalithiasis affecting the posterior SCC, but can also affect the anterior and, very rarely, the horizontal canal (Baloh et al., 1993; De la Meilleure et al., 1996).

Figure 13.3 The Hallpike-Dix test for diagnosis of benign paroxysmal positional vertigo (BPPV).

Table 13.3 Oculomotor and positional tests of the vestibular patient

Oculomotor examination	Details and expected findings
Spontaneous nystagmus Room light (visual fixation) Frenzel lenses (no visual fixation)	For the first four tests the patient is asked to hold the head stationary. Patient looks straight ahead. The eyes are observed for a nystagmus and the direction is noted. Frenzel lenses both remove visual fixation and magnify the eyes (Figure 13. 9). Nystagmus due to an acute unilateral peripheral vestibular disorder will have a fast phase away from the side of the lesion (Figure 13.2) and will be suppressed by visual fixation (i.e. focusing on something). Thus it is unlikely to be seen without Frenzel Lenses.
Gaze evoked nystagmus*	Patient is asked to watch examiner’s finger as it moves from left to right (about 30°) stopping at 30°. Normally the eyes will remain steady on the examiner’s finger. If abnormal the eyes will make saccadic movements in an effort to remain on the examiner’s finger.
Smooth pursuit*	Ability to track examiners moving finger, from side to side and up and down with the eyes when the head is stationary. Normally the eyes make smooth movements, abnormalities include slow or saccadic movements of the eyes.
Saccades*	The examiner holds two objects and asks the patient to look from one to the other (left to right, right to left, up to down and down to up starting from a mid position and moving about 30°). An abnormal response would be that the eyes over or under shoot the target
VOR cancellation*	Ability to suppress the vestibulo-ocular reflex and move the eyes in phase with the head. Patient is asked to follow a moving target as the examiner moves the head in the same direction.
Vestibulo-Ocular reflex- Halmagyi head thrust test (Halmagyi & Curthoys, 1988; Halmagyi et al., 2001) Slow head movement Fast head movement	A normal VOR is when the eyes are able to stay fixated on a stationary target when the head moves. The patient is asked to keep their eyes steady on a target (usually the examiner’s nose) whilst the examiner moves patient’s head in a small range of movement (about 30°) from side to side and then up and down slowly. This is repeated with faster movements of the head. Patients with vestibular deficits are unable to keep the eyes steady and may use a saccadic movement to return their eyes to the target. For example in right vestibular hypofunction, if the head is moved to the right, the eyes may make a saccadic movement to the left. Abnormalities are more often seen with faster head movements.
Fukuda Step Test (Fukuda, 1959)	Also known as Unterberger’s test. The patient is asked to close their eyes and march with high steps on the spot for 50 steps which they count themselves. The examiner stands behind the patient to ensure patient safety. The patient is observed for rotation and/or progression forwards from the start position. It is considered abnormal if the patient rotates more than 30° or progresses forwards more than 50 cm
Dyanmic Visual Acuity (Tian et al., 2002)	Tests visual acuity when the head is moving and is an indicator of VOR function. The patient is first asked to read a Snellen chart and static visual acuity is ascertained. The examiner then moves the head from side to side at a frequency of 1-2hz (using a metronome) and the patient then is asked to read a Snellen chart again. If visual acuity changes by more than 3 lines, acuity during head movement is considered impaired.
Positional tests Hallpike-Dix test (Figure 13.3)	The patient is long sitting on plinth with eyes open. The head is turned 45° to the side that is being tested. The patient is brought quickly into a lying position by the examiner until the cervical spine is in 30° of extension. This position is maintained for 50 seconds and the presence, duration and direction of nystagmus is noted. Symptoms are also noted. This test is diagnostic for BPPV. A positive finding is nystagmus (most commonly torsional towards the tested side) that comes on with a latency, may stay or disappear, and attenuates with repeated testing.

* Abnormality detected during these tests is indicative of central nervous system pathology.

Patients with BPPV complain of vertigo associated with certain head movements, i.e. rolling over in bed, looking up, bending down, and will usually avoid these movements. BPPV is more common in older patients.

Ménière’s disease

The cause of Ménière’s disease is an increase in volume and a problem with absorption of the endolymph (one of the fluids in the inner ear). This results in dilation of the endolymphatic spaces (endolymphatic hydrops). This happens episodically and an attack is characterized by a complaint of a fullness in the ear, reduction of hearing and tinnitus (a ringing sound in the ear). This is followed by vertigo, vomiting and postural imbalance and nystagmus is observed. The episodes may last from 30 minutes to 72 hours and then the patient gradually improves. Episodes are generally managed with medication, diet and rest, but in severe cases surgery may be indicated (see below). Although it was formerly thought vestibular rehabilitation was not indicated in patients with Ménière’s, as attacks remit spontaneously, there is now some evidence to suggest it has a role in those patients who present with complaints of impaired balance between attacks (Gottshall et al., 2005).

Bilateral vestibular hypofunction

This condition can be caused by infections, e.g. meningitis, tumours (e.g. bilateral acoustic neuromas in neurofibromatosis), Ménière’s disease, autoimmune diseases and ototoxic drugs (e.g. aminoglycoside antibiotics). In some cases the cause is unknown. Patients with bilateral vestibular hypofunction do not usually complain of vertigo when vestibular loss is symmetrical. Their main problems include balance and gait impairments and decreased gaze stability due to loss of VOR function. They complain that they cannot see clearly during head movements and describe their surroundings as bouncing or jumping. This is termed oscillopsia.

Recovery from vestibular pathology: vestibular compensation

In most cases, the symptoms of patients with a unilateral vestibular loss spontaneously ameliorate over a period of weeks. The process by which the patient recovers is called vestibular compensation. The spontaneous nystagmus disappears by 2–3 days (static compensation) and the symptoms associated with movement (vertigo, visual blurring and postural unsteadiness) by 6 weeks (dynamic compensation). Hair cells have not been shown to regenerate in humans; therefore the patient must recover by other means.

Research has shown that plastic changes occur in the CNS in response to peripheral vestibular pathology and these changes are responsible for vestibular compensation (Curthoys, 2000; Zee, 2000). Three processes are thought to contribute:

1. Initially, the cerebellum inhibits firing of the vestibular nuclei of the unaffected side, probably to reduce the asymmetry produced by the lesion. The vestibular nucleus of the affected side begins spontaneously to fire tonically again, probably due to neurochemical changes produced by the loss of input (denervation supersensitivity; Curthoys, 2000).

2. The second process is known as sensory substitution. In this process the CNS reorganizes to substitute or utilize inputs more efficiently from intact systems, including vision and somatosensory and cervical proprioceptive systems. For example in slower head movements, saccadic movement of the eyes can be recruited to assist a poor VOR to help maintain stable vision (Schubert et al., 2008). An increase in muscle spindle input from the neck proprioceptors has also been demonstrated (Strupp et al., 1998a). The intact vestibular end organ is able to compensate somewhat for loss on the other side, as both sides respond to head movement in any direction. It is important to note also that if there is some remaining vestibular function on the pathological side, the CNS will utilize it.

3. Lastly, the process of habituation is thought to play a role in vestibular compensation. Habituation is generally defined as a reduction in response over time with repeated exposure to a specific stimulus. This is the process thought to underpin improvement with the Cawthorne Cooksey exercises (see below), in which the patient repeatedly performs head and/or eye movements that provoke symptoms of vertigo.

The reasons why some patients fail to compensate are not always clear, but may be a result of abnormality in the CNS, visual, somatosensory or musculoskeletal systems. Animal studies have shown that compensation is delayed by immobilization, reduced or absent visual inputs and is promoted by exercise (Courjon et al., 1977; Lacour et al., 1997). It is thought that the CNS needs to experience the error signals in order for vestibular compensation to occur. Certain medications, including those used in the treatment of vestibular problems, can delay compensation (Zee, 1985). An intact CNS is vitally important for the process of vestibular compensation and thus patients with central vestibular problems will have a slower and more incomplete recovery (Rudge & Chambers, 1982). In bilateral vestibular loss, there may be no remaining VOR function with which to compensate, so the process of sensory substitution plays a major role in the recovery of these patients and recovery will always be incomplete.

Key point

Most patients with unilateral peripheral vestibular pathology spontaneously recover over a period of a few weeks through a process known as vestibular compensation. Patients who do not spontaneously recover present for treatment and may benefit from vestibular rehabilitation.