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Abnormalities of muscle tone and movement
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Abnormalities of muscle tone and movement T Britton
INTRODUCTION CHAPTER CONTENTS Introduction 47 Muscle tone 47 Hypertonia 48 Hypotonia 52 Movement disorders 52 General terms for movement disorders 52 Tremor 53 Myoclonus 54 Chorea 54 Ballismus 54 Dystonia 54 Ataxia 55 Other disorders of movement 55 References 56
This chapter presents an overview of the abnormalities of muscle tone and movement seen in patients with neurological disorders. The nature and proposed mechanisms of the abnormalities, the disorders in which they commonly occur and their medical treatment are outlined. Physical management is discussed in Chapter 25. Specialist texts in which further details can be found include those by Adams & Victor (2001), Weiner & Laing (1989) and Rothwell (1994).
MUSCLE TONE Muscle tone can be defined clinically as the resistance that is encountered when the joint of a relaxed patient is moved passively. (This is the usual clinical definition of muscle tone, though there is no universally accepted definition. Physiologists, in particular, use ‘tone’ in a different way – to signify a state of muscle tension or continuous muscle activity.) In practice, the clinician (medical practitioner or physiotherapist) usually assesses muscle tone in one of two ways. He or she may grasp a patient’s relaxed limb and try to move it, noting the amount of effort required to overcome the resistance – the muscle tone. Alternatively, the clinician may observe how a limb responds to being shaken or to being released suddenly: the greater the resistance to movement (i.e. the greater the muscle tone), the more rigidly the limb will behave. The resistance encountered when moving the joint of a relaxed individual is a combination of the passive stiffness of the joint and its surrounding soft tissues plus any active muscle tension, especially that due to stretch reflex contraction. The passive stiffness is dependent upon the inherent viscoelastic properties of the tissues
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and varies with age and other physiological parameters (e.g. limb temperature, preceding exercise). The contribution of active stretch reflex contractions to overall muscle tone also varies considerably, even in normal individuals, being particularly influenced by the age and emotional state of the person, as well as whether tone is assessed at a proximal or distal joint. All of the many factors that can affect normal muscle tone need to be taken into account before the clinician decides whether muscle tone is abnormal and this requires considerable skill. The assessment of muscle tone is an important and valuable part of the clinical examination and allows useful deductions to be made about the state of the nervous system. Clinically, muscle tone may be abnormally increased (hypertonia) or decreased (hypotonia). In principle, hypertonia or hypotonia may arise either as a consequence of changes in the passive stiffness of the joint and its surrounding soft tissues or because of changes in the amount contributed by active muscle contractions. Most clinical and neurophysiological research has hitherto concentrated on the latter mechanism (in particular, muscle contractions reflexively evoked by muscle stretch), but there is increasing awareness of the potential importance of changes in passive joint stiffness.
Spasticity may be defined as a velocity-dependent increase in resistance to passive stretch of a muscle, with exaggerated tendon reflexes (Lance, 1990).
individual patient will depend upon the site of the neurological lesion (cerebral hemisphere, brainstem or spinal cord), the presence of internal (e.g. a full bladder) or external stimuli and on the patient’s overall posture (i.e. sitting or lying). Stretching the muscle of a patient with spasticity results in an abnormally large reflex contraction. The more rapidly the examiner moves the limb of a patient with spasticity, the greater the increase in muscle tone. Indeed, the resistance to movement may become so great as to stop all movement, the abrupt cessation of movement being described clinically as a ‘catch’. If passive flexion of the arm or extension of the leg continues, the resistance to movement may then disappear rapidly. The catch, followed by the sudden melting away of resistance, is referred to clinically as the ‘claspknife phenomenon’. In certain situations, sustained rhythmic contractions can be generated when a muscle is stretched rapidly and the tension maintained. The rhythmic contractions, which are usually at a frequency of 5–7 Hz, are termed ‘clonus’. Clonus is most commonly seen at the ankle when the foot is dorsiflexed (ankle clonus). It can also be seen at the knee (patellar clonus) and occasionally at other sites in the body. The pathologically brisk tendon reflexes that are typically associated with spasticity are further evidence of the increased responsiveness of muscle to stretch. The pathophysiological mechanisms involved in the response to brief phasic stretches almost certainly differ from those involved in the response to slower stretches discussed in the paragraph above (Sheean, 2002). Pathologically brisk tendon reflexes may spread or irradiate to other muscles or muscle groups (Adams & Victor, 2001). Thus, a tap on the Achilles tendon not only evokes a pathologically brisk ankle jerk but may also produce reflex contractions in the proximal muscles such as the hamstrings, quadriceps and hip adductor muscles.
Clinical features Spasticity is recognised clinically by:
Clinical significance Spasticity is one of the cardinal
1. the characteristic pattern of involvement of certain muscle groups 2. the increased responsiveness of muscles to stretch 3. the associated finding of markedly increased
features of an upper motor neurone syndrome. The presence of spasticity should therefore always lead to a search for lesions of the upper motor neurone anywhere from the motor cortex to the spinal motoneurones. Common causes of spasticity include cerebrovascular disease (Ch. 6), brain damage (Chs 7 and 18), spinal cord compression (Chs 8 and 19) and inflammatory lesions of the spinal cord such as those found in multiple sclerosis (Ch. 10).
Hypertonia Two main types of hypertonia are recognised: spasticity and rigidity. These differ in their cause and clinical significance. Two rare types of hypertonia, gegenhalten and alpha-rigidity, are also discussed briefly.
Spasticity
tendon reflexes. Spasticity predominantly affects the antigravity muscles, i.e. the flexors of the arms and the extensors of the legs. As a result, the spastic upper limb tends to assume a flexed and pronated posture whilst a spastic lower limb is usually held extended and adducted, a posture that is characteristically seen (on the affected side) in hemiplegic patients following a stroke (see Ch. 6). However, spasticity is not always associated with such a posture. The actual posture adopted by any
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Pathophysiological mechanisms of spasticity The pathological basis of spasticity is the abnormal enhancement of spinal stretch reflexes. What causes the enhancement of spinal stretch reflexes is less certain. In principle, they could be enhanced by increased muscle spindle
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sensitivity (mediated via increased gamma-motoneurone drive) or by increased excitability of central synapses involved in the reflex arc. Microneurographic studies in humans and neurophysiological studies in experimental animals have found no abnormality in the sensitivity of the muscle spindle in established spasticity (Burke, 1983; PierrotDeseilligny & Mazieres, 1985). Muscle spindle sensitivity may be increased in the early stages of an upper motor neurone lesion, but then return to normal. Increased excitability of central synapses involved in the reflex arc therefore appears to be the main factor determining the enhancement of spinal stretch reflexes (Thilmann et al., 1991; Dietz, 1992; Singer et al., 2001). How does an upper motor neurone lesion alter the excitability of central synapses involved in the stretch reflex arc? In the short term, it seems that previously inactive (or silent) spinal synapses can become active following the disruption of descending motor inputs, thereby increasing the efficiency of the reflex arc (PierrotDeseilligny & Mazieres, 1985). In the longer term, the synapses of descending motor pathways on spinal motoneurones and interneurones degenerate and are replaced by sprouting of the remaining intraspinal synapses, again increasing the efficiency of the reflex arc (Tsukahara & Murakami, 1983; Noth, 1991). Reading the preceding paragraphs might lead one to believe that spasticity was simply a release phenomenon, caused by the removal of inhibitory descending influences on the spinal cord. Such an impression, however, would be wrong. The true situation is almost certainly more complicated. Removal of inhibitory descending influences is undoubtedly important but spasticity also occurs in the presence of facilitatory descending influences. The facilitatory descending pathways may be responsible for the continuous muscle activity that can be seen in the upper motor neurone syndrome and which is not dependent on the stretch reflex. There are many descending pathways that arise in the brainstem and influence spinal cord excitability (see Ch. 1). For simplicity, these descending pathways can be divided into two main groups on the basis of their anatomy and physiology. One group, comprising the pontine and lateral bulbar reticulospinal pathways, along with the vestibulospinal pathways (although the functional contribution of the latter is probably limited in humans), descends in the ventral funiculus of the spinal cord and tends to facilitate muscle tone. The other group, comprising mainly the crossed reticulospinal pathways from the ventromedial bulbar reticular formation, descends in the lateral funiculus (just behind the corticospinal tracts) and tends to inhibit muscle tone. Evidence from humans and experimental animals suggests that normal muscle tone depends on a balance
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between the facilitatory and inhibitory systems (Brown, 1994; Sheean, 2002). Spasticity may arise if the inhibitory pathways are interrupted or if there is increased activity in the facilitatory pathways. Spasticity following lesions of the frontal cerebral cortex or internal capsule probably results from loss of cortical drive to the bulbar inhibitory centre (thereby reducing activity in the inhibitory crossed reticulospinal pathways and releasing the spinal stretch reflex). Such spasticity is often noted to be less severe than that associated with spinal cord disease. The usually severe spasticity associated with spinal cord disease may be due in part to the close proximity of the crossed reticulospinal pathways and the corticospinal pathways within the spinal cord. The above discussion has concentrated on the neural and stretch reflex changes that accompany spasticity. Such changes are undoubtedly of prime importance. However, there is increasing awareness that established spasticity is also associated with significant changes in passive mechanical factors (Davidoff, 1992; Lin et al., 1994; Given et al., 1995; O’Dwyer et al., 1996). With weakness and disuse, muscles undergo shortening with a reduction in the number of sarcomeres and an increase in collagen content (Williams et al., 1988). They also tend to have a decreasing proportion of type II muscle fibres (Dattola et al., 1993). All of these changes lead to an increase in the passive stiffness of the joint and (to the clinician) a feeling of increased tone. The amount to which passive stiffness contributes to the feeling of increased tone varies from patient to patient, which may explain why it has proved so difficult to produce a device to measure spasticity automatically (Damiano et al., 2002). The changes in the passive mechanical factors associated with spasticity are of practical importance. All clinicians know of the difficulty of dealing with established contractures in patients with spasticity. It has been proposed that such contractures are the result of a vicious circle. The increased gain of the stretch reflex loop causes the muscle to shorten. The shortened muscle then undergoes remodelling, losing some of its sarcomeres. Unless there is some intervention to stretch or lengthen the muscle, this process will continue, leading to contracture (see Ch. 25). If this model were correct, then the most appropriate treatment would be regular stretching of affected muscles (e.g. stretching exercises). Such treatment might be assisted with the judicious use of muscle relaxants or botulinum toxin injections. In contrast, tendon-lengthening operations would not appear to be ideal, since the (released) muscle would continue to lose its sarcomeres and therefore shorten further. However, tendon-lengthening operations do allow the joint to assume a more natural position, thereby often increasing limb function and allowing
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Table 4.1 Comparison of spasticity and rigidity Spasticity
Rigidity
Pattern of muscle Upper-limb flexors; involvement lower-limb extensors
Flexors and extensors equally
Nature of tone
Velocity-dependent increase in tone; ‘clasp-knife’ phenomenon
Constant throughout movement; ‘lead pipe’
Tendon reflexes
Increased
Normal
Pathophysiology
Increased spinal stretch reflex gain
Increased longlatency component of stretch reflex
Clinical significance
Upper motor neurone (pyramidal) sign
Extrapyramidal sign
the antagonist muscles to work at less mechanical disadvantage. A more recently proposed cause of shortening in pennate muscles is fibre atrophy, leading to shortening of the aponeurosis (Shortland et al., 2002). If this model were operating, strengthening exercises would be appropriate. The mechanism and clinical implications of this proposed phenomenon are discussed in Chapters 29 (p. 495) and 30 (p. 512). The clinical and pathophysiological features of spasticity are summarised and contrasted with those of rigidity in Table 4.1.
Pharmacological treatment Details of the drugs mentioned in this section are given in Chapter 28. The mainstay of treatment for spasticity is baclofen. Baclofen is believed to act on inhibitory GABA-B receptors within the spinal cord, reducing the gain of the stretch reflex loop. Like all drugs that are used in the treatment of spasticity, baclofen may uncover or exacerbate muscle weakness. Patients often rely on their spasticity for support and when it is reduced they find that their limbs are floppy and weak. Baclofen also causes drowsiness and tiredness, which can be lessened if the drug is given intrathecally by pump. Benzodiazepines (e.g. diazepam, clonazepam) are also used in the treatment of spasticity, but are generally less favoured than baclofen because of their potential to produce addiction. They are believed to act on inhibitory GABA-A receptors within the spinal cord. Dantrolene acts directly on muscle to produce weakness by inhibiting excitation–contraction coupling. It is rarely used on its own but may be used in conjunction with baclofen or benzodiazepines. Hepatotoxicity can be a problem with dantrolene. 50
Tizanidine is an alpha-2 agonist that decreases presynaptic activity in excitatory interneurones. It is claimed to cause (or uncover) less muscle weakness than baclofen, but hepatotoxicity may be a problem. Botulinum toxin injections have been used to weaken muscles selectively. The results in adult patients with spasticity are mixed, but there may be a role for botulinum toxin in patients with severe adductor spasms (Hyman et al., 2000). More favourable results have been obtained in children with spastic cerebral palsy (Cosgrove et al., 1994). Experimental work in mice suggests that botulinum toxin injections may reduce the risk of developing contractures (Cosgrove & Graham, 1994). Intrathecal phenol blocks are occasionally used in patients with severe lower-limb spasticity to help control pain or improve posture (Beckerman et al., 1996). The risk of non-specific damage to other neural structures is high, and such treatment is therefore usually restricted to patients who have no useful lower-limb function or sphincter control.
Rigidity Rigidity is another cause of increased tone, which can occur in different forms. It should be noted that the terms ‘decerebrate rigidity’ and ‘decorticate rigidity’ describe abnormal posturing associated with coma rather than a specific type of hypertonia. The more correct terms would therefore be ‘decerebrate and decorticate posturing’. Decerebrate posturing occurs with a variety of acute and subacute brainstem disorders and consists of opisthotonus, clenched jaws and stiffly extended limbs. The abnormal postures are characteristically triggered by passive movements of the limbs or neck or by any noxious stimulus. Decorticate posturing occurs with high or midbrain lesions (or above) and consists of flexion of the upper limb and extension of the legs similar to that of a spastic tetraplegia.
Clinical features Rigidity is recognised clinically as an increased resistance to relatively slowly imposed passive movements. It is present in both extensor and flexor muscle groups. Typically the examiner will flex and extend the wrist slowly and may describe the resistance as being of ‘lead pipe’ type, reflecting the fact that the resistance is felt throughout the movement (in distinction to spasticity where the resistance initially increases rapidly and then melts away – the so-called clasp-knife phenomenon). It should be emphasised that the imposed movements must be slow: use of more rapid movements, that would be appropriate for examining spasticity, may result in the erroneous conclusion that the tone is normal. Tendon reflexes are normal, in contrast to the hyperreflexia associated with spasticity.
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Many patients with rigidity have an additional tremor as part of their extrapyramidal disorder. When this is so, the tremor will be felt superimposed on the rigidity, giving rise to the clinical phenomenon of ‘cogwheel rigidity’. Rigidity may be appreciated in the limbs or axially. One of the best ways of demonstrating axial tone is to rotate the patient’s shoulders while he or she stands relaxed. In normal individuals, the examiner will encounter little resistance and the arms will be seen to swing relatively freely. However, in patients with axial rigidity, the examiner has the feeling of trying to move a rigid structure and the arms fail to swing.
Clinical significance Rigidity is one of the cardinal features of an extrapyramidal syndrome. The term ‘parkinsonism’ is synonymous with extrapyramidal syndrome; other synonyms used include parkinsonian syndrome and akinetic–rigid syndrome. Parkinson’s disease (see Ch. 11) is a specific disease entity and is but one cause of parkinsonism. The other cardinal feature is hypokinesia/bradykinesia (reduced and slow movements, see below). Tremor is a frequent finding in parkinsonism, but is not always present. Extrapyramidal syndromes are caused by functional disturbances of the basal ganglia (caudate nucleus, putamen, globus pallidus and subthalamic nucleus). Common causes of parkinsonism include Parkinson’s disease itself, multiple system atrophy and a number of rarer conditions that are sometimes called ‘Parkinson-plus syndromes’ (e.g. progressive supranuclear palsy, corticobasal degeneration). Extrapyramidal syndromes are a not uncommon side-effect of drugs, especially the neuroleptic drugs and the so-called vestibular sedatives (e.g. metoclopramide, prochlorperazine, cinnarizine). Cerebrovascular disease rarely gives rise to true parkinsonism. However, cerebrovascular disease affecting the frontal lobes may give rise to a superficially similar clinical syndrome, with gait dyspraxia (which can be mistaken for the shuffling gait of parkinsonism) and gegenhalten, mentioned below (which may be mistaken for rigidity). The condition can be distinguished from parkinsonism by the relative preservation of upper-limb and facial movement, the lack of a significant response to levodopa, and the frequent occurrence of urinary incontinence. Pathophysiological mechanisms The pathophysiological basis of rigidity appears to be enhancement of the long-latency component of the stretch reflex (Rothwell, 1994). The normal stretch reflex can be divided into a short-latency component and a long-latency component. In patients with parkinsonian rigidity, the shortlatency (spinal) component is normal in size, reflecting
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the fact that tendon reflexes in the condition are normal. However, the long-latency component, which may take a transcortical route, is enlarged. Furthermore, the size of the long-latency component correlates with the clinical degree of rigidity: the greater the rigidity, the larger the size of the long-latency component.
Pharmacological treatment Treatment is usually focused on the underlying extrapyramidal syndrome rather than the rigidity per se. It is always important to check whether the patient is taking any neuroleptic medication that could be causing or exacerbating the condition. Parkinson’s disease itself is usually treated with levodopa or a dopamine agonist drug (Ch. 11). Levodopa is generally given in conjunction with a peripheral dopadecarboxylase inhibitor to prevent the drug’s metabolism in the gut and to increase its availability to the brain. The initial response to levodopa is usually very gratifying. Unfortunately, longer-term treatment may be associated with a less satisfactory clinical response and the development of troublesome side effects, including involuntary movements and psychiatric disturbance. Dopamine agonist drugs are believed to produce fewer motor side-effects (i.e. involuntary movements) but are also probably less effective at relieving extrapyramidal symptoms and signs. Other drugs used in the treatment of Parkinson’s disease include catecholO-methyltransferase inhibitors, anticholinergics and selegiline. The same drugs are also frequently used in the treatment of other (non-Parkinson’s disease) extrapyramidal syndromes, but the clinical response is generally less impressive.
Gegenhalten Some elderly patients find it difficult to relax their limbs during examination. When attempting to examine tone, the patients appear to resist movement voluntarily but they are unable to prevent such movement and it is not therefore voluntary resistance. This phenomenon is usually termed ‘gegenhalten’ (Adams & Victor, 2001). Gegenhalten is usually caused by damage to the frontal lobes of the brain, and may be seen in association with cerebrovascular disease or neurodegenerative conditions such as Alzheimer’s disease. Cognitive impairment, grasp reflexes and other primitive reflexes are frequent accompaniments.
Alpha-rigidity In some patients, tone may be increased in a rigid fashion (being present equally in both flexor and extensor muscles), but their tendon reflexes are absent or reduced. It is as though there is increased motor unit excitability
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in the absence of the spinal reflex arc. Such a condition may be seen in association with spinal cord lesions, particularly those affecting the central grey matter. Stiffperson syndrome, which is associated with antibodies against the enzyme glutamic acid decarboxylase, may produce a similar increase in muscle tone (Levy et al., 1999).
Hypotonia In the normal individual, active stretch reflex contractions contribute little to resting muscle tone. Most of the tone arises from the passive viscoelastic properties of the joints and soft tissues. Reduced tone due to central nervous system (CNS) disorders is therefore often difficult to detect clinically (because the viscoelastic properties remain unchanged). Hypotonia due to central lesions may be apparent in certain situations, however. Patients with cerebellar hypotonia characteristically have pendular tendon reflexes because of limb underdamping. Children with hypotonia due to CNS disorders are often described as floppy. Hypotonia is also seen in the acute stage of spinal cord disease or trauma (see Ch. 8). With recovery from this spinal shock, the tone increases and the reflexes return to produce the characteristic upper motor neurone syndrome. Reduced muscle tone due to peripheral nervous system disorders is usually easier to detect. This is mainly because the associated muscle wasting reduces the passive stiffness of the joint. The absence of stretch reflex contractions in lower motor neurone lesions probably contributes little to the reduction in muscle tone. When hypotonia is unequivocally present, it is usually indicative of a lower motor neurone lesion. Other features of a lower motor neurone lesion include weakness, areflexia and fasciculation.
MOVEMENT DISORDERS Clinically distinctive patterns of involuntary movements occur in many diseases. Recognising these patterns may help to identify the underlying disorder. The aim of the remainder of the chapter is to give brief descriptions of the common movement disorders and their clinical significance. First, however, it may be helpful to define some general terms.
Akinesia, hypokinesia and bradykinesia Akinesia, hypokinesia and bradykinesia are often used loosely and inaccurately (Berardelli et al., 2001). Akinesia is the absence of movement while hypokinesia describes abnormally decreased movement. Bradykinesia refers to slowness of movement. Akinesia, hypokinesia and bradykinesia are cardinal features of extrapyramidal disease, to the extent that some neurologists refer to parkinsonism as an akinetic–rigid syndrome. It should be noted, however, that akinesia, hypokinesia and bradykinesia are not used when there is paresis (either upper or lower motor neurone) to account for the deficient or absent movements. Basal ganglia and frontal lobe dysfunction, particularly the supplementary motor area, are thought to underlie akinesia, hypokinesia and bradykinesia (Berardelli et al., 2001). Clinically, patients with Parkinson’s disease are slow in initiating movement (the patient may take longer than normal to respond) and also by slowness in carrying out a task. When such a patient is called from the outpatient waiting room, he or she will often take a long time to rise from the chair and then walk slowly from the waiting room into the clinic room itself. Part of the problem with walking is that people with parkinsonism tend to take shorter steps than is normal. Indeed, the amplitudes of all their movements tend to be smaller than required for optimal performance. In the upper limb, bradykinesia can most easily be demonstrated by asking the patient to open and close his or her fist as quickly as possible.
Dyskinesias and hyperkinesia Some neurological diseases are associated with additional (involuntary) movements. Such involuntary movements are best termed dyskinesias and include myoclonus, chorea, ballism, dystonia, tic and tremor (Table 4.2). Some neurologists describe these conditions as hyperkinesias rather than dyskinesias in order to distinguish them from hypokinetic movement disorders (e.g. parkinsonism). However, confusion may then arise when a patient with (hypokinetic) Parkinson’s disease develops (hyperkinetic) tremor or chorea. A further problem with the use of the term ‘hyperkinesia’ is that it is sometimes assumed that hyperkinetic movements are faster than normal. This is not the case (and hyperkinesia is not the converse of bradykinesia). Indeed, in most so-called hyperkinetic movement disorders, movement velocities are actually slower than normal. The term ‘dyskinesia’ is therefore preferred to hyperkinesia.
General terms for movement disorders The terms discussed here describe the amount and speed of movement, as well as some involuntary movements.
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Hypometria and hypermetria Movements that are smaller than intended are described as hypometric. Patients with Parkinson’s
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Table 4.2 Main causes of some dyskinetic movement disorders Tremor Rest tremor
Parkinson’s disease Drug-induced parkinsonism Other extrapyramidal disease
Action tremor
Enhanced physiological tremor (e.g. anxiety, alcohol, hyperthyroidism) Essential tremor Cerebellar disease Wilson’s disease
Intention tremor
Brainstem or cerebellar disease (e.g. multiple sclerosis, spinocerebellar degeneration)
Myoclonus Without encephalopathy With encephalopathy Non-progressive Progressive
Juvenile myoclonic epilepsy Myoclonic epilepsy Postanoxic myoclonus Storage disorders (e.g. Lafora body disease) Unverricht–Lundborg disease Metabolic encephalopathies (e.g. respiratory, renal and liver failure) Creutzfeldt–Jakob disease
Chorea Sydenham’s chorea Pregnancy-associated chorea Contraceptive pill-associated chorea Huntington’s disease Thyrotoxicosis Systemic lupus erythematosus Drug-induced chorea (e.g. neuroleptics, phenytoin) Dystonia Generalised
Hemidystonia
Idiopathic torsion dystonia Drug-induced Athetoid cerebral palsy Wilson’s disease Metabolic storage disorders Dopa-responsive dystonia Basal ganglia lesions (e.g. tumours, vascular, postthalamotomy)
disease often have hypometric movements. In contrast, patients with cerebellar disease may overshoot the target, producing so-called hypermetric movements.
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Tremor Tremor is best defined as any unwanted, rhythmic, approximately sinusoidal movement of a limb or body part (Elble & Koller, 1990). The fact that the movement is unwanted distinguishes tremor from voluntary oscillatory movements such as waving or writing. Its rhythmic and approximately sinusoidal character distinguishes it from myoclonus and chorea. The term ‘myorhythmia’ is occasionally used to signify a slow tremor of relatively large amplitude that affects the proximal part of a limb. Clinically, tremor is usually classified according to the situation in which it occurs (Bain, 1993). Examples of types of tremor and the conditions in which they occur are given in Table 4.2. A tremor that is present when the limb is relaxed and fully supported is called a rest tremor. Action tremors occur when the patient attempts to maintain a posture (postural tremor) or to move (kinetic tremor). Tremor which gets worse at the end of a movement is called an intention or terminal tremor and is associated with cerebellar dysfunction. There is no satisfactory pathological classification of tremor. A rest tremor almost always suggests parkinsonism. Postural tremors have many causes but are most commonly due to enhanced physiological tremor or essential tremor. All of us have a fine postural tremor (physiological tremor) of which we are usually completely unaware. Physiological tremor may become noticeable, however, in certain situations (e.g. anxiety, fear, thyrotoxicosis, fatigue, use of adrenergic drugs). This noticeable tremor is called enhanced physiological tremor. Essential tremor is suggested by the finding of a symmetrical postural upper-limb tremor that is absent at rest and is not made strikingly worse by movement (and in the absence of factors that might enhance physiological tremor). In a substantial proportion of patients with essential tremor, there is a family history of similarly affected relatives and up to half the patients may find temporary amelioration of their tremor with alcohol. For a discussion of other tremors the reader is referred to Elble & Koller (1990) and Bain (1993). The pathophysiological mechanisms responsible for tremor are poorly understood. The nervous system, like all mechanical systems, has a natural tendency to oscillate. This tendency is due in part to the mechanical properties of the limbs and in part to neural feedback loops. Neuropathological studies have demonstrated physical and biochemical changes in brains from patients with different disorders involving tremor but have failed to elucidate the precise changes that can be attributed to the symptom of tremor (Bain, 1993). Recent evidence suggests that cerebellar mechanisms
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are of central importance to the maintenance and generation of essential tremor (Britton, 1995).
Myoclonus Myoclonus describes brief shock-like jerks of a limb or body part. Myoclonic jerks may be restricted to one part of the body (focal myoclonus) or may be generalised (generalised myoclonus). Jerks can occur spontaneously or with movement, or they may be reflexly triggered by light, sound, touch or tendon taps. Following a myoclonic jerk there is a lapse of posture that is associated with electrical silence in the muscles, lasting for around 200 ms (Shibasaki, 1995). Lapses in posture can sometimes occur without a noticeable preceding jerk. Such postural lapses are called asterixis and typically occur with metabolic encephalopathies (e.g. in respiratory, renal or liver failure). Neurophysiologically, there are three main types of myoclonus: cortical myoclonus, which arises from the cerebral cortex; reticular reflex myoclonus, which arises from the brainstem; and propriospinal myoclonus, which arises from the spinal cord. Neurophysiological studies are of special help in the assessment of patients with myoclonus (Shibasaki, 1995). Cortical myoclonus is preceded by an electrical ‘spike’ over the contralateral motor cortex (normal movements, even fast movements, are never preceded by an electrical spike). The jerks are focal and can often be triggered by touching the affected limb (cortical reflex myoclonus). The condition responds to anticonvulsants and piracetam. Occasionally, there may be repetitive bursts of cortical myoclonus. Such repetitive bursts are in essence a focal epileptic discharge. Neurophysiological studies in reticular reflex myoclonus show that the abnormal electrical activity arises from the brainstem. Such jerks are symmetrical and generalised. They may be triggered by a startle (e.g. unexpected noise or light) and the jerks themselves have a number of similarities to an exaggerated startle response. Some patients with spinal cord disease have abnormal jerks that begin at one segmental level and then spread to neighbouring segments. Such patients have spinal myoclonus. Myoclonus is a feature of many neurological diseases. Most patients are found to have a progressive, usually degenerative, encephalopathy. Postanoxic myoclonus occurs, as its name suggests, after a respiratory arrest, especially in patients with chronic lung conditions. After recovery, such patients develop severe myoclonic jerking, especially in their legs, and they walk with a characteristic bouncy gait. There are often additional cerebellar signs and the condition is presumed to arise because of damage to the large (and
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hence oxygen-demanding) cerebellar Purkinje cells (see Ch. 1, p. 16). The condition is treated with valproate and 5-hydroxytryptamine.
Chorea Patients with disease of the basal ganglia may develop frequent jerky movements that constantly flit from one part of the body to another. Such movements are termed ‘chorea’. The movements flit randomly around the body, in contrast to myoclonus, which tends to affect the same part or parts of the body. The absence of sustained abnormal posturing distinguishes the condition from dystonia. Chorea occurs in a range of basal ganglia diseases, including Wilson’s disease, Huntington’s disease (see Ch. 12), polycythaemia, thyrotoxicosis, systemic lupus erythematosus, cerebrovascular disease and several other rarer neurodegenerative conditions. Sydenham’s chorea is still occasionally seen following streptococcal infection in the UK. Pregnancy and the oral contraceptive pill are also associated with chorea. Chorea can be a side-effect of chronic neuroleptic medication. Where possible, the underlying cause of chorea should be treated. Chorea itself may respond to tetrabenazine, a drug that depletes presynaptic dopamine stores. Neuroleptic medication is also used.
Ballismus Violent, large-amplitude, involuntary movements of the limbs are called ballismus, or, if they affect only one side of the body, hemiballismus. These movements are often so large that they throw the patient off balance. They are continuous and may lead to exhaustion and even death. The usual cause of ballismus is cerebrovascular disease (Berardelli, 1995). It can be treated with tetrabenazine.
Dystonia Dystonia (previously known as athetosis) describes a condition where limbs or body parts are twisted into abnormal postures by sustained muscle activity. Typically, dystonia is brought out by attempted movement. However, despite the contorted posturing, such patients are often able to accomplish remarkably skilled tasks. Dystonia may be generalised, affecting the whole body, or localised, affecting a single body part or segment. Dystonia affecting just one side of the body is termed ‘hemidystonia’ and is of clinical significance because its presence should lead to a search for a lesion in the contralateral basal ganglia. Generalised dystonia is most commonly due to idiopathic torsion dystonia. The condition usually begins in
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childhood and affects the legs first. Most cases are inherited in an autosomal dominant fashion, most commonly being linked to the DYT1 gene (Misbahuddin & Warner, 2001). Dystonia is also seen following actual or presumed cerebral insults at or around the time of birth; a diagnosis of dystonic (athetoid) cerebral palsy may be made in such circumstances. More rarely, generalised dystonia may be a manifestation of a recognised metabolic disease or storage disorder. There is a rare type of familial dystonia called dopa-responsive dystonia with diurnal fluctuations. This condition responds exquisitely to levodopa. Dopa-responsive dystonia has recently been shown to result from an abnormality in the synthesis of tetrahydrobiopterin (Nygaard, 1995). Focal dystonias usually begin in adult life and commonly affect the eyes (blepharospasm), neck (torticollis) or upper limb. The legs are rarely affected. Upper-limb dystonia may be task-specific and may be the cause of some occupational cramps. Standard investigations rarely identify an underlying cause, although some cases may have a genetic basis. Electrophysiological recordings in dystonia show abnormal patterns of muscle activation with cocontraction of agonist and antagonist muscles (Rothwell, 1994). These abnormalities seem to be due to reduced reciprocal inhibition. When a muscle is activated voluntarily, its antagonist muscles normally relax. The relaxation of antagonist muscles depends in part upon reciprocal inhibition: afferent impulses from the activated muscle inhibit the firing of motoneurones subserving antagonists. In patients with dystonia, reciprocal inhibition is reduced and cocontraction occurs. Various treatments have been used in dystonia, including drugs (especially anticholinergics, neuroleptics, tetrabenazine), botulinum toxin injections and surgery (section of nerves and roots). Botulinum toxin is the treatment of choice for blepharospasm (a focal dystonia of facial muscles causing involuntary eye closure) and is often very beneficial in torticollis.
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the patient touches the examiner’s finger as gently as possible. Although it is relatively easy for an experienced clinician to recognise ataxia, it is much harder to analyse exactly what about the ataxic patient’s movements is abnormal. Several features seem to contribute but none is pathognomonic. Patients tend to make hypermetric movements, i.e. their limbs move farther than the desired target. They also tend to use too much force. The mechanisms that normally bring a movement to a smooth halt are abnormal and tremor commonly results. The movements of ataxic patients are also slower than normal. The significance of ataxia is that it is almost invariably associated with disease of the cerebellum or its brainstem connections (Adams & Victor, 2001). Common causes of ataxia include multiple sclerosis (see Ch. 10), Friedreich’s ataxia, alcohol and posterior fossa tumours. Less common causes include paraneoplastic syndromes and a variety of neurodegenerative conditions, some of which are hereditary (e.g. the spinocerebellar ataxias and Friedreich’s ataxia).
Other disorders of movement The following are abnormal movements that are associated with different neurological disorders.
Hemifacial spasm Hemifacial spasm describes unilateral twitching of facial muscles due to an irritative lesion of the facial nerve. The eye winks and the corner of the mouth on the affected side elevates. There may be mild facial weakness. It responds well to botulinum toxin injections. Some patients have neurosurgery to reposition blood vessels that impinge on the facial nerve.
Orofacial dyskinesias Ataxia Ataxia describes a disturbance in the co-ordination of movement. Movements are clumsy and the gait is unsteady with a wide base and reeling quality. Posture may also be affected, such that there are irregular jerky movements of the trunk when sitting (truncal ataxia or disequilibrium). In addition, there may be a limb tremor which generally gets worse towards the end of a goal-directed movement – so-called intention tremor. The latter can be brought out by asking the patient alternately to touch the examiner’s finger and then his or her own nose: the task is one of accuracy and not speed and can be made more difficult by ensuring that
Orofacial dyskinesias are commonly seen in the elderly as a complication of neuroleptic treatment. They consist of involuntary lip-smacking and chewing movements, occasionally associated with tongue protrusion. Neuroleptic medication should be avoided. Tetrabenazine may provide some benefit.
Palatal myoclonus (tremor) Some patients develop involuntary rhythmical elevation of the soft palate, which produces an audible click and interferes with speech. Some cases are associated with hypertrophy of the inferior olivary nucleus in the brainstem.
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Tics Tics are involuntary movements or vocalisations that patients may be able to suppress temporarily at the expense of increasing inner tension. The movements can be simple, e.g. a twitch of the face or arm, or more
complex, when they may appear semipurposeful. Tics are associated with obsessive–compulsive disorders and the Gilles de la Tourette syndrome. Neuroleptic medication may be required.
References Adams RD, Victor M. Principles of Neurology. New York: McGraw-Hill; 2001. Bain P. A combined clinical and neurophysiological approach to the study of patients with tremor. J Neurol Neurosurg Psychiatry 1993, 56:839–844. Beckerman H, Lankhorst GJ, Verbeek ALM, et al. The effects of phenol nerve and muscle blocks in treating spasticity: review of the literature. Crit Rev Rehab 1996, 8:111–124. Berardelli A. Symptomatic or secondary basal ganglia diseases and tardive dyskinesias. Curr Opin Neurol 1995, 8:320–322. Berardelli A, Rothwell JC, Thompson PD, Hallett M. Pathophysiology of bradykinesia in Parkinson’s disease. Brain 2001, 124:2131–2146. Britton TC. Essential tremor and its variants. Curr Opin Neurol 1995, 8:314–319. Brown P. Spasticity. J Neurol Neurosurg Psychiatry 1994, 57:773–777. Burke D. Critical examination of the case for and against fusimotor involvement in disorders of muscle tone. Adv Neurol 1983, 39:133–150. Cosgrove AP, Corry IS, Graham HK. Botulinum toxin in the management of the lower limb in cerebral palsy. Dev Med Child Neurol 1994, 36:386–396. Cosgrove AP, Graham HK. Botulinum toxin A prevents the development of contractures in the hereditary spastic mouse. Dev Med Child Neurol 1994, 36:379–385. Damiano DL, Quinlivan JM, Owen BF et al. What does the Ashworth scale really measure and are instrumented measures more valid and precise? Dev Med Child Neurol 2002, 44:112–118. Dattola R, Girlanda P, Vita G et al. Muscle rearrangement in patients with hemiparesis after stroke: an electrophysiological and morphological study. Eur Neurol 1993, 33:109–114. Davidoff RA. Skeletal muscle tone and the misunderstood stretch reflex. Neurology 1992, 42:951–963. Dietz V. Human neuronal control of automatic functional movements: interaction between central programs and afferent input. Physiol Rev 1992, 72:33–69. Elble RJ, Koller WC. Tremor. Baltimore: Johns Hopkins University Press; 1990. Given JD, Dewald JP, Rymer WZ. Joint dependent passive stiffness in paretic and contralateral limbs of spastic patients with hemiparetic stroke. J Neurol Neurosurg Psychiatry 1995, 59:271–279. Hyman N, Barnes M, Bhakta B et al. Botulinum toxin (Dysport) treatment of hip adductor spasticity in multiple sclerosis: a prospective, randomized, double-blind,
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placebo controlled, dose ranging study. J Neurol Neurosurg Psychiatry 2000, 68:707–712. Lance JW. What is spasticity? Lancet 1990, 335:606. Levy LM, Dalakas MC, Floeter MK. The stiff-person syndrome: an autoimmune disorder affecting neurotransmission of gamma-aminobutyric acid. Ann Intern Med 1999, 131:523–524. Lin JP, Brown JK, Brotherstone R. Assessment of spasticity in hemiplegic cerebral palsy. II: Distal lower-limb reflex excitability and function. Dev Med Child Neurol 1994, 36:290–303. Misbahuddin A, Warner TT. Dystonia: an update on genetics and treatment. Curr Opin Neurol 2001, 14:471–475. Noth J. Trends in the pathophysiology and pharmacology of spasticity. J Neurol 1991, 238:131–139. Nygaard TG. Dopa-responsive dystonia. Curr Opin Neurol 1995, 8:310–313. O’Dwyer NJ, Ada L, Neilson PD. Spasticity and muscle contracture following stroke. Brain 1996, 119:1737–1749. Pierrot-Deseilligny E, Mazieres L. Spinal mechanisms underlying spasticity. In: Delwaide PJ, Young RR, eds. Clinical Neurophysiology in Spasticity. Amsterdam: Elsevier; 1985:63–76. Rothwell JC. Control of Human Voluntary Movement, 2nd edn. London: Chapman & Hall; 1994. Sheean G. The pathophysiology of spasticity. Eur J Neurol 2002, 9 (Suppl. 1):3–9. Shibasaki H. Myoclonus. Curr Opin Neurol 1995, 8:331–334. Shortland AP, Harris CA, Gough M et al. Architecture of the medial gastrocnemius in children with spastic diplegia. Dev Med Child Neurol 2002, 44:158–163. Singer B, Dunne J, Allison G. Reflex and non-reflex elements of hypertonia in triceps surae muscles following acquired brain injury: implications for rehabilitation. Disabil Rehab 2001, 23:749–757. Thilmann AF, Fellows SJ, Garms E. The mechanism of spastic muscle hypertonus. Variation in reflex gain over the time course of spasticity. Brain 1991, 114:233–244. Tsukahara N, Murakami F. Axonal sprouting and recovery of function after brain damage. Adv Neurol 1983, 39:1073–1084. Warner TT, Fletcher NA, Davis MB et al. Linkage analysis in British and French families with idiopathic torsion dystonia. Brain 1993, 116:739–744. Weiner WJ, Lang AE. Movement Disorders: A Comprehensive Survey. New York: Futura; 1989. Williams PE, Catanese T, Lucey EG, Goldspink G. The importance of stretch and contractile activity in the prevention of connective tissue accumulation in muscle. J Anat 1988, 158:109–114.
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Abnormalities of muscle tone and movement T Britton
INTRODUCTION CHAPTER CONTENTS Introduction 47 Muscle tone 47 Hypertonia 48 Hypotonia 52 Movement disorders 52 General terms for movement disorders 52 Tremor 53 Myoclonus 54 Chorea 54 Ballismus 54 Dystonia 54 Ataxia 55 Other disorders of movement 55 References 56
This chapter presents an overview of the abnormalities of muscle tone and movement seen in patients with neurological disorders. The nature and proposed mechanisms of the abnormalities, the disorders in which they commonly occur and their medical treatment are outlined. Physical management is discussed in Chapter 25. Specialist texts in which further details can be found include those by Adams & Victor (2001), Weiner & Laing (1989) and Rothwell (1994).
MUSCLE TONE Muscle tone can be defined clinically as the resistance that is encountered when the joint of a relaxed patient is moved passively. (This is the usual clinical definition of muscle tone, though there is no universally accepted definition. Physiologists, in particular, use ‘tone’ in a different way – to signify a state of muscle tension or continuous muscle activity.) In practice, the clinician (medical practitioner or physiotherapist) usually assesses muscle tone in one of two ways. He or she may grasp a patient’s relaxed limb and try to move it, noting the amount of effort required to overcome the resistance – the muscle tone. Alternatively, the clinician may observe how a limb responds to being shaken or to being released suddenly: the greater the resistance to movement (i.e. the greater the muscle tone), the more rigidly the limb will behave. The resistance encountered when moving the joint of a relaxed individual is a combination of the passive stiffness of the joint and its surrounding soft tissues plus any active muscle tension, especially that due to stretch reflex contraction. The passive stiffness is dependent upon the inherent viscoelastic properties of the tissues
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and varies with age and other physiological parameters (e.g. limb temperature, preceding exercise). The contribution of active stretch reflex contractions to overall muscle tone also varies considerably, even in normal individuals, being particularly influenced by the age and emotional state of the person, as well as whether tone is assessed at a proximal or distal joint. All of the many factors that can affect normal muscle tone need to be taken into account before the clinician decides whether muscle tone is abnormal and this requires considerable skill. The assessment of muscle tone is an important and valuable part of the clinical examination and allows useful deductions to be made about the state of the nervous system. Clinically, muscle tone may be abnormally increased (hypertonia) or decreased (hypotonia). In principle, hypertonia or hypotonia may arise either as a consequence of changes in the passive stiffness of the joint and its surrounding soft tissues or because of changes in the amount contributed by active muscle contractions. Most clinical and neurophysiological research has hitherto concentrated on the latter mechanism (in particular, muscle contractions reflexively evoked by muscle stretch), but there is increasing awareness of the potential importance of changes in passive joint stiffness.
Spasticity may be defined as a velocity-dependent increase in resistance to passive stretch of a muscle, with exaggerated tendon reflexes (Lance, 1990).
individual patient will depend upon the site of the neurological lesion (cerebral hemisphere, brainstem or spinal cord), the presence of internal (e.g. a full bladder) or external stimuli and on the patient’s overall posture (i.e. sitting or lying). Stretching the muscle of a patient with spasticity results in an abnormally large reflex contraction. The more rapidly the examiner moves the limb of a patient with spasticity, the greater the increase in muscle tone. Indeed, the resistance to movement may become so great as to stop all movement, the abrupt cessation of movement being described clinically as a ‘catch’. If passive flexion of the arm or extension of the leg continues, the resistance to movement may then disappear rapidly. The catch, followed by the sudden melting away of resistance, is referred to clinically as the ‘claspknife phenomenon’. In certain situations, sustained rhythmic contractions can be generated when a muscle is stretched rapidly and the tension maintained. The rhythmic contractions, which are usually at a frequency of 5–7 Hz, are termed ‘clonus’. Clonus is most commonly seen at the ankle when the foot is dorsiflexed (ankle clonus). It can also be seen at the knee (patellar clonus) and occasionally at other sites in the body. The pathologically brisk tendon reflexes that are typically associated with spasticity are further evidence of the increased responsiveness of muscle to stretch. The pathophysiological mechanisms involved in the response to brief phasic stretches almost certainly differ from those involved in the response to slower stretches discussed in the paragraph above (Sheean, 2002). Pathologically brisk tendon reflexes may spread or irradiate to other muscles or muscle groups (Adams & Victor, 2001). Thus, a tap on the Achilles tendon not only evokes a pathologically brisk ankle jerk but may also produce reflex contractions in the proximal muscles such as the hamstrings, quadriceps and hip adductor muscles.
Clinical features Spasticity is recognised clinically by:
Clinical significance Spasticity is one of the cardinal
1. the characteristic pattern of involvement of certain muscle groups 2. the increased responsiveness of muscles to stretch 3. the associated finding of markedly increased
features of an upper motor neurone syndrome. The presence of spasticity should therefore always lead to a search for lesions of the upper motor neurone anywhere from the motor cortex to the spinal motoneurones. Common causes of spasticity include cerebrovascular disease (Ch. 6), brain damage (Chs 7 and 18), spinal cord compression (Chs 8 and 19) and inflammatory lesions of the spinal cord such as those found in multiple sclerosis (Ch. 10).
Hypertonia Two main types of hypertonia are recognised: spasticity and rigidity. These differ in their cause and clinical significance. Two rare types of hypertonia, gegenhalten and alpha-rigidity, are also discussed briefly.
Spasticity
tendon reflexes. Spasticity predominantly affects the antigravity muscles, i.e. the flexors of the arms and the extensors of the legs. As a result, the spastic upper limb tends to assume a flexed and pronated posture whilst a spastic lower limb is usually held extended and adducted, a posture that is characteristically seen (on the affected side) in hemiplegic patients following a stroke (see Ch. 6). However, spasticity is not always associated with such a posture. The actual posture adopted by any
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Pathophysiological mechanisms of spasticity The pathological basis of spasticity is the abnormal enhancement of spinal stretch reflexes. What causes the enhancement of spinal stretch reflexes is less certain. In principle, they could be enhanced by increased muscle spindle
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sensitivity (mediated via increased gamma-motoneurone drive) or by increased excitability of central synapses involved in the reflex arc. Microneurographic studies in humans and neurophysiological studies in experimental animals have found no abnormality in the sensitivity of the muscle spindle in established spasticity (Burke, 1983; PierrotDeseilligny & Mazieres, 1985). Muscle spindle sensitivity may be increased in the early stages of an upper motor neurone lesion, but then return to normal. Increased excitability of central synapses involved in the reflex arc therefore appears to be the main factor determining the enhancement of spinal stretch reflexes (Thilmann et al., 1991; Dietz, 1992; Singer et al., 2001). How does an upper motor neurone lesion alter the excitability of central synapses involved in the stretch reflex arc? In the short term, it seems that previously inactive (or silent) spinal synapses can become active following the disruption of descending motor inputs, thereby increasing the efficiency of the reflex arc (PierrotDeseilligny & Mazieres, 1985). In the longer term, the synapses of descending motor pathways on spinal motoneurones and interneurones degenerate and are replaced by sprouting of the remaining intraspinal synapses, again increasing the efficiency of the reflex arc (Tsukahara & Murakami, 1983; Noth, 1991). Reading the preceding paragraphs might lead one to believe that spasticity was simply a release phenomenon, caused by the removal of inhibitory descending influences on the spinal cord. Such an impression, however, would be wrong. The true situation is almost certainly more complicated. Removal of inhibitory descending influences is undoubtedly important but spasticity also occurs in the presence of facilitatory descending influences. The facilitatory descending pathways may be responsible for the continuous muscle activity that can be seen in the upper motor neurone syndrome and which is not dependent on the stretch reflex. There are many descending pathways that arise in the brainstem and influence spinal cord excitability (see Ch. 1). For simplicity, these descending pathways can be divided into two main groups on the basis of their anatomy and physiology. One group, comprising the pontine and lateral bulbar reticulospinal pathways, along with the vestibulospinal pathways (although the functional contribution of the latter is probably limited in humans), descends in the ventral funiculus of the spinal cord and tends to facilitate muscle tone. The other group, comprising mainly the crossed reticulospinal pathways from the ventromedial bulbar reticular formation, descends in the lateral funiculus (just behind the corticospinal tracts) and tends to inhibit muscle tone. Evidence from humans and experimental animals suggests that normal muscle tone depends on a balance
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between the facilitatory and inhibitory systems (Brown, 1994; Sheean, 2002). Spasticity may arise if the inhibitory pathways are interrupted or if there is increased activity in the facilitatory pathways. Spasticity following lesions of the frontal cerebral cortex or internal capsule probably results from loss of cortical drive to the bulbar inhibitory centre (thereby reducing activity in the inhibitory crossed reticulospinal pathways and releasing the spinal stretch reflex). Such spasticity is often noted to be less severe than that associated with spinal cord disease. The usually severe spasticity associated with spinal cord disease may be due in part to the close proximity of the crossed reticulospinal pathways and the corticospinal pathways within the spinal cord. The above discussion has concentrated on the neural and stretch reflex changes that accompany spasticity. Such changes are undoubtedly of prime importance. However, there is increasing awareness that established spasticity is also associated with significant changes in passive mechanical factors (Davidoff, 1992; Lin et al., 1994; Given et al., 1995; O’Dwyer et al., 1996). With weakness and disuse, muscles undergo shortening with a reduction in the number of sarcomeres and an increase in collagen content (Williams et al., 1988). They also tend to have a decreasing proportion of type II muscle fibres (Dattola et al., 1993). All of these changes lead to an increase in the passive stiffness of the joint and (to the clinician) a feeling of increased tone. The amount to which passive stiffness contributes to the feeling of increased tone varies from patient to patient, which may explain why it has proved so difficult to produce a device to measure spasticity automatically (Damiano et al., 2002). The changes in the passive mechanical factors associated with spasticity are of practical importance. All clinicians know of the difficulty of dealing with established contractures in patients with spasticity. It has been proposed that such contractures are the result of a vicious circle. The increased gain of the stretch reflex loop causes the muscle to shorten. The shortened muscle then undergoes remodelling, losing some of its sarcomeres. Unless there is some intervention to stretch or lengthen the muscle, this process will continue, leading to contracture (see Ch. 25). If this model were correct, then the most appropriate treatment would be regular stretching of affected muscles (e.g. stretching exercises). Such treatment might be assisted with the judicious use of muscle relaxants or botulinum toxin injections. In contrast, tendon-lengthening operations would not appear to be ideal, since the (released) muscle would continue to lose its sarcomeres and therefore shorten further. However, tendon-lengthening operations do allow the joint to assume a more natural position, thereby often increasing limb function and allowing
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Table 4.1 Comparison of spasticity and rigidity Spasticity
Rigidity
Pattern of muscle Upper-limb flexors; involvement lower-limb extensors
Flexors and extensors equally
Nature of tone
Velocity-dependent increase in tone; ‘clasp-knife’ phenomenon
Constant throughout movement; ‘lead pipe’
Tendon reflexes
Increased
Normal
Pathophysiology
Increased spinal stretch reflex gain
Increased longlatency component of stretch reflex
Clinical significance
Upper motor neurone (pyramidal) sign
Extrapyramidal sign
the antagonist muscles to work at less mechanical disadvantage. A more recently proposed cause of shortening in pennate muscles is fibre atrophy, leading to shortening of the aponeurosis (Shortland et al., 2002). If this model were operating, strengthening exercises would be appropriate. The mechanism and clinical implications of this proposed phenomenon are discussed in Chapters 29 (p. 495) and 30 (p. 512). The clinical and pathophysiological features of spasticity are summarised and contrasted with those of rigidity in Table 4.1.
Pharmacological treatment Details of the drugs mentioned in this section are given in Chapter 28. The mainstay of treatment for spasticity is baclofen. Baclofen is believed to act on inhibitory GABA-B receptors within the spinal cord, reducing the gain of the stretch reflex loop. Like all drugs that are used in the treatment of spasticity, baclofen may uncover or exacerbate muscle weakness. Patients often rely on their spasticity for support and when it is reduced they find that their limbs are floppy and weak. Baclofen also causes drowsiness and tiredness, which can be lessened if the drug is given intrathecally by pump. Benzodiazepines (e.g. diazepam, clonazepam) are also used in the treatment of spasticity, but are generally less favoured than baclofen because of their potential to produce addiction. They are believed to act on inhibitory GABA-A receptors within the spinal cord. Dantrolene acts directly on muscle to produce weakness by inhibiting excitation–contraction coupling. It is rarely used on its own but may be used in conjunction with baclofen or benzodiazepines. Hepatotoxicity can be a problem with dantrolene. 50
Tizanidine is an alpha-2 agonist that decreases presynaptic activity in excitatory interneurones. It is claimed to cause (or uncover) less muscle weakness than baclofen, but hepatotoxicity may be a problem. Botulinum toxin injections have been used to weaken muscles selectively. The results in adult patients with spasticity are mixed, but there may be a role for botulinum toxin in patients with severe adductor spasms (Hyman et al., 2000). More favourable results have been obtained in children with spastic cerebral palsy (Cosgrove et al., 1994). Experimental work in mice suggests that botulinum toxin injections may reduce the risk of developing contractures (Cosgrove & Graham, 1994). Intrathecal phenol blocks are occasionally used in patients with severe lower-limb spasticity to help control pain or improve posture (Beckerman et al., 1996). The risk of non-specific damage to other neural structures is high, and such treatment is therefore usually restricted to patients who have no useful lower-limb function or sphincter control.
Rigidity Rigidity is another cause of increased tone, which can occur in different forms. It should be noted that the terms ‘decerebrate rigidity’ and ‘decorticate rigidity’ describe abnormal posturing associated with coma rather than a specific type of hypertonia. The more correct terms would therefore be ‘decerebrate and decorticate posturing’. Decerebrate posturing occurs with a variety of acute and subacute brainstem disorders and consists of opisthotonus, clenched jaws and stiffly extended limbs. The abnormal postures are characteristically triggered by passive movements of the limbs or neck or by any noxious stimulus. Decorticate posturing occurs with high or midbrain lesions (or above) and consists of flexion of the upper limb and extension of the legs similar to that of a spastic tetraplegia.
Clinical features Rigidity is recognised clinically as an increased resistance to relatively slowly imposed passive movements. It is present in both extensor and flexor muscle groups. Typically the examiner will flex and extend the wrist slowly and may describe the resistance as being of ‘lead pipe’ type, reflecting the fact that the resistance is felt throughout the movement (in distinction to spasticity where the resistance initially increases rapidly and then melts away – the so-called clasp-knife phenomenon). It should be emphasised that the imposed movements must be slow: use of more rapid movements, that would be appropriate for examining spasticity, may result in the erroneous conclusion that the tone is normal. Tendon reflexes are normal, in contrast to the hyperreflexia associated with spasticity.
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Many patients with rigidity have an additional tremor as part of their extrapyramidal disorder. When this is so, the tremor will be felt superimposed on the rigidity, giving rise to the clinical phenomenon of ‘cogwheel rigidity’. Rigidity may be appreciated in the limbs or axially. One of the best ways of demonstrating axial tone is to rotate the patient’s shoulders while he or she stands relaxed. In normal individuals, the examiner will encounter little resistance and the arms will be seen to swing relatively freely. However, in patients with axial rigidity, the examiner has the feeling of trying to move a rigid structure and the arms fail to swing.
Clinical significance Rigidity is one of the cardinal features of an extrapyramidal syndrome. The term ‘parkinsonism’ is synonymous with extrapyramidal syndrome; other synonyms used include parkinsonian syndrome and akinetic–rigid syndrome. Parkinson’s disease (see Ch. 11) is a specific disease entity and is but one cause of parkinsonism. The other cardinal feature is hypokinesia/bradykinesia (reduced and slow movements, see below). Tremor is a frequent finding in parkinsonism, but is not always present. Extrapyramidal syndromes are caused by functional disturbances of the basal ganglia (caudate nucleus, putamen, globus pallidus and subthalamic nucleus). Common causes of parkinsonism include Parkinson’s disease itself, multiple system atrophy and a number of rarer conditions that are sometimes called ‘Parkinson-plus syndromes’ (e.g. progressive supranuclear palsy, corticobasal degeneration). Extrapyramidal syndromes are a not uncommon side-effect of drugs, especially the neuroleptic drugs and the so-called vestibular sedatives (e.g. metoclopramide, prochlorperazine, cinnarizine). Cerebrovascular disease rarely gives rise to true parkinsonism. However, cerebrovascular disease affecting the frontal lobes may give rise to a superficially similar clinical syndrome, with gait dyspraxia (which can be mistaken for the shuffling gait of parkinsonism) and gegenhalten, mentioned below (which may be mistaken for rigidity). The condition can be distinguished from parkinsonism by the relative preservation of upper-limb and facial movement, the lack of a significant response to levodopa, and the frequent occurrence of urinary incontinence. Pathophysiological mechanisms The pathophysiological basis of rigidity appears to be enhancement of the long-latency component of the stretch reflex (Rothwell, 1994). The normal stretch reflex can be divided into a short-latency component and a long-latency component. In patients with parkinsonian rigidity, the shortlatency (spinal) component is normal in size, reflecting
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the fact that tendon reflexes in the condition are normal. However, the long-latency component, which may take a transcortical route, is enlarged. Furthermore, the size of the long-latency component correlates with the clinical degree of rigidity: the greater the rigidity, the larger the size of the long-latency component.
Pharmacological treatment Treatment is usually focused on the underlying extrapyramidal syndrome rather than the rigidity per se. It is always important to check whether the patient is taking any neuroleptic medication that could be causing or exacerbating the condition. Parkinson’s disease itself is usually treated with levodopa or a dopamine agonist drug (Ch. 11). Levodopa is generally given in conjunction with a peripheral dopadecarboxylase inhibitor to prevent the drug’s metabolism in the gut and to increase its availability to the brain. The initial response to levodopa is usually very gratifying. Unfortunately, longer-term treatment may be associated with a less satisfactory clinical response and the development of troublesome side effects, including involuntary movements and psychiatric disturbance. Dopamine agonist drugs are believed to produce fewer motor side-effects (i.e. involuntary movements) but are also probably less effective at relieving extrapyramidal symptoms and signs. Other drugs used in the treatment of Parkinson’s disease include catecholO-methyltransferase inhibitors, anticholinergics and selegiline. The same drugs are also frequently used in the treatment of other (non-Parkinson’s disease) extrapyramidal syndromes, but the clinical response is generally less impressive.
Gegenhalten Some elderly patients find it difficult to relax their limbs during examination. When attempting to examine tone, the patients appear to resist movement voluntarily but they are unable to prevent such movement and it is not therefore voluntary resistance. This phenomenon is usually termed ‘gegenhalten’ (Adams & Victor, 2001). Gegenhalten is usually caused by damage to the frontal lobes of the brain, and may be seen in association with cerebrovascular disease or neurodegenerative conditions such as Alzheimer’s disease. Cognitive impairment, grasp reflexes and other primitive reflexes are frequent accompaniments.
Alpha-rigidity In some patients, tone may be increased in a rigid fashion (being present equally in both flexor and extensor muscles), but their tendon reflexes are absent or reduced. It is as though there is increased motor unit excitability
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in the absence of the spinal reflex arc. Such a condition may be seen in association with spinal cord lesions, particularly those affecting the central grey matter. Stiffperson syndrome, which is associated with antibodies against the enzyme glutamic acid decarboxylase, may produce a similar increase in muscle tone (Levy et al., 1999).
Hypotonia In the normal individual, active stretch reflex contractions contribute little to resting muscle tone. Most of the tone arises from the passive viscoelastic properties of the joints and soft tissues. Reduced tone due to central nervous system (CNS) disorders is therefore often difficult to detect clinically (because the viscoelastic properties remain unchanged). Hypotonia due to central lesions may be apparent in certain situations, however. Patients with cerebellar hypotonia characteristically have pendular tendon reflexes because of limb underdamping. Children with hypotonia due to CNS disorders are often described as floppy. Hypotonia is also seen in the acute stage of spinal cord disease or trauma (see Ch. 8). With recovery from this spinal shock, the tone increases and the reflexes return to produce the characteristic upper motor neurone syndrome. Reduced muscle tone due to peripheral nervous system disorders is usually easier to detect. This is mainly because the associated muscle wasting reduces the passive stiffness of the joint. The absence of stretch reflex contractions in lower motor neurone lesions probably contributes little to the reduction in muscle tone. When hypotonia is unequivocally present, it is usually indicative of a lower motor neurone lesion. Other features of a lower motor neurone lesion include weakness, areflexia and fasciculation.
MOVEMENT DISORDERS Clinically distinctive patterns of involuntary movements occur in many diseases. Recognising these patterns may help to identify the underlying disorder. The aim of the remainder of the chapter is to give brief descriptions of the common movement disorders and their clinical significance. First, however, it may be helpful to define some general terms.
Akinesia, hypokinesia and bradykinesia Akinesia, hypokinesia and bradykinesia are often used loosely and inaccurately (Berardelli et al., 2001). Akinesia is the absence of movement while hypokinesia describes abnormally decreased movement. Bradykinesia refers to slowness of movement. Akinesia, hypokinesia and bradykinesia are cardinal features of extrapyramidal disease, to the extent that some neurologists refer to parkinsonism as an akinetic–rigid syndrome. It should be noted, however, that akinesia, hypokinesia and bradykinesia are not used when there is paresis (either upper or lower motor neurone) to account for the deficient or absent movements. Basal ganglia and frontal lobe dysfunction, particularly the supplementary motor area, are thought to underlie akinesia, hypokinesia and bradykinesia (Berardelli et al., 2001). Clinically, patients with Parkinson’s disease are slow in initiating movement (the patient may take longer than normal to respond) and also by slowness in carrying out a task. When such a patient is called from the outpatient waiting room, he or she will often take a long time to rise from the chair and then walk slowly from the waiting room into the clinic room itself. Part of the problem with walking is that people with parkinsonism tend to take shorter steps than is normal. Indeed, the amplitudes of all their movements tend to be smaller than required for optimal performance. In the upper limb, bradykinesia can most easily be demonstrated by asking the patient to open and close his or her fist as quickly as possible.
Dyskinesias and hyperkinesia Some neurological diseases are associated with additional (involuntary) movements. Such involuntary movements are best termed dyskinesias and include myoclonus, chorea, ballism, dystonia, tic and tremor (Table 4.2). Some neurologists describe these conditions as hyperkinesias rather than dyskinesias in order to distinguish them from hypokinetic movement disorders (e.g. parkinsonism). However, confusion may then arise when a patient with (hypokinetic) Parkinson’s disease develops (hyperkinetic) tremor or chorea. A further problem with the use of the term ‘hyperkinesia’ is that it is sometimes assumed that hyperkinetic movements are faster than normal. This is not the case (and hyperkinesia is not the converse of bradykinesia). Indeed, in most so-called hyperkinetic movement disorders, movement velocities are actually slower than normal. The term ‘dyskinesia’ is therefore preferred to hyperkinesia.
General terms for movement disorders The terms discussed here describe the amount and speed of movement, as well as some involuntary movements.
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Hypometria and hypermetria Movements that are smaller than intended are described as hypometric. Patients with Parkinson’s
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Table 4.2 Main causes of some dyskinetic movement disorders Tremor Rest tremor
Parkinson’s disease Drug-induced parkinsonism Other extrapyramidal disease
Action tremor
Enhanced physiological tremor (e.g. anxiety, alcohol, hyperthyroidism) Essential tremor Cerebellar disease Wilson’s disease
Intention tremor
Brainstem or cerebellar disease (e.g. multiple sclerosis, spinocerebellar degeneration)
Myoclonus Without encephalopathy With encephalopathy Non-progressive Progressive
Juvenile myoclonic epilepsy Myoclonic epilepsy Postanoxic myoclonus Storage disorders (e.g. Lafora body disease) Unverricht–Lundborg disease Metabolic encephalopathies (e.g. respiratory, renal and liver failure) Creutzfeldt–Jakob disease
Chorea Sydenham’s chorea Pregnancy-associated chorea Contraceptive pill-associated chorea Huntington’s disease Thyrotoxicosis Systemic lupus erythematosus Drug-induced chorea (e.g. neuroleptics, phenytoin) Dystonia Generalised
Hemidystonia
Idiopathic torsion dystonia Drug-induced Athetoid cerebral palsy Wilson’s disease Metabolic storage disorders Dopa-responsive dystonia Basal ganglia lesions (e.g. tumours, vascular, postthalamotomy)
disease often have hypometric movements. In contrast, patients with cerebellar disease may overshoot the target, producing so-called hypermetric movements.
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Tremor Tremor is best defined as any unwanted, rhythmic, approximately sinusoidal movement of a limb or body part (Elble & Koller, 1990). The fact that the movement is unwanted distinguishes tremor from voluntary oscillatory movements such as waving or writing. Its rhythmic and approximately sinusoidal character distinguishes it from myoclonus and chorea. The term ‘myorhythmia’ is occasionally used to signify a slow tremor of relatively large amplitude that affects the proximal part of a limb. Clinically, tremor is usually classified according to the situation in which it occurs (Bain, 1993). Examples of types of tremor and the conditions in which they occur are given in Table 4.2. A tremor that is present when the limb is relaxed and fully supported is called a rest tremor. Action tremors occur when the patient attempts to maintain a posture (postural tremor) or to move (kinetic tremor). Tremor which gets worse at the end of a movement is called an intention or terminal tremor and is associated with cerebellar dysfunction. There is no satisfactory pathological classification of tremor. A rest tremor almost always suggests parkinsonism. Postural tremors have many causes but are most commonly due to enhanced physiological tremor or essential tremor. All of us have a fine postural tremor (physiological tremor) of which we are usually completely unaware. Physiological tremor may become noticeable, however, in certain situations (e.g. anxiety, fear, thyrotoxicosis, fatigue, use of adrenergic drugs). This noticeable tremor is called enhanced physiological tremor. Essential tremor is suggested by the finding of a symmetrical postural upper-limb tremor that is absent at rest and is not made strikingly worse by movement (and in the absence of factors that might enhance physiological tremor). In a substantial proportion of patients with essential tremor, there is a family history of similarly affected relatives and up to half the patients may find temporary amelioration of their tremor with alcohol. For a discussion of other tremors the reader is referred to Elble & Koller (1990) and Bain (1993). The pathophysiological mechanisms responsible for tremor are poorly understood. The nervous system, like all mechanical systems, has a natural tendency to oscillate. This tendency is due in part to the mechanical properties of the limbs and in part to neural feedback loops. Neuropathological studies have demonstrated physical and biochemical changes in brains from patients with different disorders involving tremor but have failed to elucidate the precise changes that can be attributed to the symptom of tremor (Bain, 1993). Recent evidence suggests that cerebellar mechanisms
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are of central importance to the maintenance and generation of essential tremor (Britton, 1995).
Myoclonus Myoclonus describes brief shock-like jerks of a limb or body part. Myoclonic jerks may be restricted to one part of the body (focal myoclonus) or may be generalised (generalised myoclonus). Jerks can occur spontaneously or with movement, or they may be reflexly triggered by light, sound, touch or tendon taps. Following a myoclonic jerk there is a lapse of posture that is associated with electrical silence in the muscles, lasting for around 200 ms (Shibasaki, 1995). Lapses in posture can sometimes occur without a noticeable preceding jerk. Such postural lapses are called asterixis and typically occur with metabolic encephalopathies (e.g. in respiratory, renal or liver failure). Neurophysiologically, there are three main types of myoclonus: cortical myoclonus, which arises from the cerebral cortex; reticular reflex myoclonus, which arises from the brainstem; and propriospinal myoclonus, which arises from the spinal cord. Neurophysiological studies are of special help in the assessment of patients with myoclonus (Shibasaki, 1995). Cortical myoclonus is preceded by an electrical ‘spike’ over the contralateral motor cortex (normal movements, even fast movements, are never preceded by an electrical spike). The jerks are focal and can often be triggered by touching the affected limb (cortical reflex myoclonus). The condition responds to anticonvulsants and piracetam. Occasionally, there may be repetitive bursts of cortical myoclonus. Such repetitive bursts are in essence a focal epileptic discharge. Neurophysiological studies in reticular reflex myoclonus show that the abnormal electrical activity arises from the brainstem. Such jerks are symmetrical and generalised. They may be triggered by a startle (e.g. unexpected noise or light) and the jerks themselves have a number of similarities to an exaggerated startle response. Some patients with spinal cord disease have abnormal jerks that begin at one segmental level and then spread to neighbouring segments. Such patients have spinal myoclonus. Myoclonus is a feature of many neurological diseases. Most patients are found to have a progressive, usually degenerative, encephalopathy. Postanoxic myoclonus occurs, as its name suggests, after a respiratory arrest, especially in patients with chronic lung conditions. After recovery, such patients develop severe myoclonic jerking, especially in their legs, and they walk with a characteristic bouncy gait. There are often additional cerebellar signs and the condition is presumed to arise because of damage to the large (and
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hence oxygen-demanding) cerebellar Purkinje cells (see Ch. 1, p. 16). The condition is treated with valproate and 5-hydroxytryptamine.
Chorea Patients with disease of the basal ganglia may develop frequent jerky movements that constantly flit from one part of the body to another. Such movements are termed ‘chorea’. The movements flit randomly around the body, in contrast to myoclonus, which tends to affect the same part or parts of the body. The absence of sustained abnormal posturing distinguishes the condition from dystonia. Chorea occurs in a range of basal ganglia diseases, including Wilson’s disease, Huntington’s disease (see Ch. 12), polycythaemia, thyrotoxicosis, systemic lupus erythematosus, cerebrovascular disease and several other rarer neurodegenerative conditions. Sydenham’s chorea is still occasionally seen following streptococcal infection in the UK. Pregnancy and the oral contraceptive pill are also associated with chorea. Chorea can be a side-effect of chronic neuroleptic medication. Where possible, the underlying cause of chorea should be treated. Chorea itself may respond to tetrabenazine, a drug that depletes presynaptic dopamine stores. Neuroleptic medication is also used.
Ballismus Violent, large-amplitude, involuntary movements of the limbs are called ballismus, or, if they affect only one side of the body, hemiballismus. These movements are often so large that they throw the patient off balance. They are continuous and may lead to exhaustion and even death. The usual cause of ballismus is cerebrovascular disease (Berardelli, 1995). It can be treated with tetrabenazine.
Dystonia Dystonia (previously known as athetosis) describes a condition where limbs or body parts are twisted into abnormal postures by sustained muscle activity. Typically, dystonia is brought out by attempted movement. However, despite the contorted posturing, such patients are often able to accomplish remarkably skilled tasks. Dystonia may be generalised, affecting the whole body, or localised, affecting a single body part or segment. Dystonia affecting just one side of the body is termed ‘hemidystonia’ and is of clinical significance because its presence should lead to a search for a lesion in the contralateral basal ganglia. Generalised dystonia is most commonly due to idiopathic torsion dystonia. The condition usually begins in
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childhood and affects the legs first. Most cases are inherited in an autosomal dominant fashion, most commonly being linked to the DYT1 gene (Misbahuddin & Warner, 2001). Dystonia is also seen following actual or presumed cerebral insults at or around the time of birth; a diagnosis of dystonic (athetoid) cerebral palsy may be made in such circumstances. More rarely, generalised dystonia may be a manifestation of a recognised metabolic disease or storage disorder. There is a rare type of familial dystonia called dopa-responsive dystonia with diurnal fluctuations. This condition responds exquisitely to levodopa. Dopa-responsive dystonia has recently been shown to result from an abnormality in the synthesis of tetrahydrobiopterin (Nygaard, 1995). Focal dystonias usually begin in adult life and commonly affect the eyes (blepharospasm), neck (torticollis) or upper limb. The legs are rarely affected. Upper-limb dystonia may be task-specific and may be the cause of some occupational cramps. Standard investigations rarely identify an underlying cause, although some cases may have a genetic basis. Electrophysiological recordings in dystonia show abnormal patterns of muscle activation with cocontraction of agonist and antagonist muscles (Rothwell, 1994). These abnormalities seem to be due to reduced reciprocal inhibition. When a muscle is activated voluntarily, its antagonist muscles normally relax. The relaxation of antagonist muscles depends in part upon reciprocal inhibition: afferent impulses from the activated muscle inhibit the firing of motoneurones subserving antagonists. In patients with dystonia, reciprocal inhibition is reduced and cocontraction occurs. Various treatments have been used in dystonia, including drugs (especially anticholinergics, neuroleptics, tetrabenazine), botulinum toxin injections and surgery (section of nerves and roots). Botulinum toxin is the treatment of choice for blepharospasm (a focal dystonia of facial muscles causing involuntary eye closure) and is often very beneficial in torticollis.
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the patient touches the examiner’s finger as gently as possible. Although it is relatively easy for an experienced clinician to recognise ataxia, it is much harder to analyse exactly what about the ataxic patient’s movements is abnormal. Several features seem to contribute but none is pathognomonic. Patients tend to make hypermetric movements, i.e. their limbs move farther than the desired target. They also tend to use too much force. The mechanisms that normally bring a movement to a smooth halt are abnormal and tremor commonly results. The movements of ataxic patients are also slower than normal. The significance of ataxia is that it is almost invariably associated with disease of the cerebellum or its brainstem connections (Adams & Victor, 2001). Common causes of ataxia include multiple sclerosis (see Ch. 10), Friedreich’s ataxia, alcohol and posterior fossa tumours. Less common causes include paraneoplastic syndromes and a variety of neurodegenerative conditions, some of which are hereditary (e.g. the spinocerebellar ataxias and Friedreich’s ataxia).
Other disorders of movement The following are abnormal movements that are associated with different neurological disorders.
Hemifacial spasm Hemifacial spasm describes unilateral twitching of facial muscles due to an irritative lesion of the facial nerve. The eye winks and the corner of the mouth on the affected side elevates. There may be mild facial weakness. It responds well to botulinum toxin injections. Some patients have neurosurgery to reposition blood vessels that impinge on the facial nerve.
Orofacial dyskinesias Ataxia Ataxia describes a disturbance in the co-ordination of movement. Movements are clumsy and the gait is unsteady with a wide base and reeling quality. Posture may also be affected, such that there are irregular jerky movements of the trunk when sitting (truncal ataxia or disequilibrium). In addition, there may be a limb tremor which generally gets worse towards the end of a goal-directed movement – so-called intention tremor. The latter can be brought out by asking the patient alternately to touch the examiner’s finger and then his or her own nose: the task is one of accuracy and not speed and can be made more difficult by ensuring that
Orofacial dyskinesias are commonly seen in the elderly as a complication of neuroleptic treatment. They consist of involuntary lip-smacking and chewing movements, occasionally associated with tongue protrusion. Neuroleptic medication should be avoided. Tetrabenazine may provide some benefit.
Palatal myoclonus (tremor) Some patients develop involuntary rhythmical elevation of the soft palate, which produces an audible click and interferes with speech. Some cases are associated with hypertrophy of the inferior olivary nucleus in the brainstem.
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Tics Tics are involuntary movements or vocalisations that patients may be able to suppress temporarily at the expense of increasing inner tension. The movements can be simple, e.g. a twitch of the face or arm, or more
complex, when they may appear semipurposeful. Tics are associated with obsessive–compulsive disorders and the Gilles de la Tourette syndrome. Neuroleptic medication may be required.
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