MOVEMENT DISORDERS

MOVEMENT DISORDERS

Disorders of movement form a substantial part of neurodegenerative diseases. They divide broadly into akinetic-rigid syndromes; slowed movement with increased tone (also called parkinsonism), and dyskinesias - added, uncontrollable movements. Precise anatomical and neurotransmitter profile changes are hard to define. Both parkinsonism and dyskinesia may coexist, leading to confusing classifications. Table 21.39 outlines the principal clinical varieties: idiopathic Parkinson's disease (an akinetic-rigid syndrome) and essential tremor (a dyskinesia) are much the commonest movement disorders.

AKINETIC-RIGID SYNDROMES

Idiopathic Parkinson's disease



Causes Movement disorders

Akinetic-rigid syndromes
Idiopathic Parkinson's disease
Drug-induced parkinsonism (e.g. phenothiazines)
MPTP-induced parkinsonism
Postencephalitic parkinsonism
Parkinsonism-plus
Childhood akinetic-rigid syndrome
Dyskinesias
Essential tremor
Chorea
Hemiballismus
Myoclonus
Tic or 'habit spasms'
Torsion dystonias
Paroxysmal dyskinesias


In 1817, James Parkinson, a physician in Hoxton, London, published The Shaking Palsy, describing this common world-wide condition, with prevalence of 150/100 000 increasing sharply in those over 70 years. Parkinson's disease is clinically and pathologically distinct from other parkinsonian syndromes.

There are few real clues as to the cause of idiopathic Parkinson's disease (PD). The relatively uniform world-wide prevalence suggests that an environmental agent is not responsible. Some factors possibly involved are:

Nicotine.

Several epidemiological studies confirm the curious fact that PD is less prevalent in tobacco smokers than in lifelong abstainers.

MPTP.

Minute doses of the pyridine compound, methylphenyltetrahydropyridine (MPTP) cause severe parkinsonism. The link between this and idiopathic PD is tenuous. Suggestions that environmental MPTP-like herbicides are implicated are entirely unsubstantiated.

Encephalitis lethargica.

Some survivors of the epidemic, presumed viral encephalitis lethargica, developed severe parkinsonism. However, it is not thought that idiopathic Parkinson's disease is related to an infective agent.

Genetic factors.

Whilst not usually familial, there is clustering of early-onset Parkinson's disease in some families. Mutations of the alpha-synuclein gene and ubiquitin carboxyl-terminal hydrolase L1 (UCHL1), on chromosomes 2p13 and 4p14-16.3 respectively, account for occasional cases. Mutations in the parkin gene on chromosome 6 have been found in families with autosomal recessive cases of PD and some young apparently sporadic cases. Parkin mutations probably account for most PD cases with onset below the age of 40. Mutant parkin proteins are unable to interact, and ubiquinate forms of α-synuclein accumulate. The relevance to the common sporadic older PD cases remains doubtful.

Pathology

In the pars compacta of the substantia nigra, progressive cell degeneration and neuronal eosinophilic inclusion bodies (Lewy bodies) are seen. These contain protein filaments of ubiquitin and alpha-synuclein. Degeneration also occurs in other basal ganglia nuclei. Biochemically there is loss of dopamine (and melanin) in the striatum. This correlates well with cell loss and with the degree of akinesia.

Clinical symptoms

The combination of tremor, rigidity and akinesia develops slowly, over months or several years, together with changes in posture. The most common initial symptoms are tremor and slowness. Patients complain that limbs and joints feel stiff. They ache. Fine movements become difficult. Slowness causes characteristic difficulty rising from a chair or getting into or out of bed. Writing becomes small (micrographia) and spidery, and tends to tail off. Relatives often notice other features - slowness and an impassive face. Idiopathic PD is almost always initially more prominent on one side.

Clinical signs

Diagnosis is usually evident from the overall appearance.

Tremor

The characteristic 4-7 Hz pill-rolling (movements between thumb and finger) rest tremor usually decreases with action. Tremor is often asymptomatic at first.

Rigidity

Stiffness develops throughout the range of limb movement and is equal in opposing muscle groups - in sharp contrast to the selective increase in tone found in spasticity. This 'lead pipe' increase in tone is usually more marked on one side. It is also present in the neck and axial muscles.

This plastic rigidity is more easily felt when a joint is moved slowly and gently. When one arm is being examined, its tone increases when the opposite arm moves actively. When stiffness occurs with tremor, smooth 'lead-pipe' rigidity is broken up into a jerky resistance to passive movement - known as cogwheeling, or cogging.

Akinesia

Poverty and slowing of movement (bradykinesia) is an additional handicap, distinct from rigidity. There is difficulty initiating movement. Rapid fine finger movements, such as piano-playing, become indistinct, slow and tremulous. Facial immobility gives a mask-like semblance of depression. The frequency of spontaneous blinking is reduced, producing a 'serpentine' stare.

Postural changes

A stoop is characteristic. Gait becomes, hurrying (festinant) and shuffling with poor arm swinging. The posture is sometimes called 'simian' to describe the ape-like forward flexion, immobility and lack of animation. Balance deteriorates, but despite this the gait retains a narrow base. Falls are common in later stages of PD, the sufferer toppling like a falling tree.

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Speech

Pronunciation is initially a monotone but progresses to characteristic tremulous slurring dysarthria, the result of combined akinesia, tremor and rigidity. Speech may eventually be lost completely (anarthria).

Gastrointestinal and other symptoms

These include heartburn, dribbling, dysphagia, constipation and weight loss. Urinary difficulties are common, especially in men. Skin is greasy and sweating excessive.

Natural history and other features

Parkinson's disease worsens over some years, beginning as a mild inconvenience but slowly progressing. Remissions are unknown except for rare and remarkable short-lived periods of release. These tend to occur at times of great emotion, fear or excitement, when the sufferer is released for seconds or minutes and able to move quickly.

While bradykinesia and tremor worsen, power remains normal until immobility makes its assessment difficult. Patients often complain bitterly of limb and joint discomfort. There is no sensory loss. The reflexes are brisk; their asymmetry follows the increase in tone. The plantar responses remain flexor. Cognitive function is preserved, at least early on. Dementia often develops in the late stages. Anxiety and depression are common.

The rate of progression is very variable, with a benign form running over several decades. Usually the course is over 10-15 years, with death resulting from bronchopneumonia.

Diagnosis

There is no laboratory test - the diagnosis is made by recognizing physical signs and distinguishing idiopathic PD from other parkinsonian syndromes. Conventional imaging (MR) is normal. Dopamine transporter imaging (available in some specialist centres) discriminates poorly - both between normal and pathological and between PD and other akinetic-rigid syndromes.

Other diffuse and multifocal brain diseases can cause features of parkinsonism, i.e. the slowing, rigidity and tremor seen in idiopathic PD. Examples are Alzheimer's disease, multi-infarct dementia, sequelae of repeated head injury (e.g. in boxers, p. 1250), and the late effects of severe hypoxia or carbon monoxide poisoning. Slowing also occurs in hypothyroidism, and in depression.

Treatment

  Levodopa crosses the blood-brain barrier, enters a neurone and is converted to dopamine.

   1. Carbidopa and benserazide reduce peripheral conversion of levodopa to dopamine by AAAD, thus reducing side-effects of excess circulating dopamine.
   2. Dietary amino acids from a high-protein meal may inhibit active transport into brain by competing with levodopa.
   3. Levodopa is converted (AAAD) to dopamine in nigrostriatal neurones.
   4. At the nerve terminal, amantadine enhances dopamine release.
   5. Dopamine agonist drugs react with dopamine receptors.
   6. Selegeline, the MAO-B inhibitor, blocks dopamine breakdown.
   7. Entacapone, a COMT inhibitor, prolongs dopamine activity by blocking breakdown.

AAAD, aromatic amino acid decarboxylase; COMT, catechol-O-methyl transferase.

While no drugs alter the course of Parkinson's disease, levodopa and/or dopaminergic agonists produce striking initial symptomatic improvement. These drugs should be avoided until they are clinically necessary because of delayed unwanted effects (see below). Catechol-O-methyl transferase inhibitors are also used as supplementary therapy. Older treatments such as the antimuscarinic trihexyphenidyl (benzhexol) helped little and frequently caused confusion; they are of some value in severe tremor. Selegeline, a monoamine oxidase B inhibitor, may delay the need for levodopa therapy by some months. Antioxidants are also used with this aim, but their value is unproven. A scheme for the mechanism of action of drugs in Parkinson's disease is shown in Figure 21.29.

Levodopa

Levodopa is combined with an aromatic amino acid decarboxylase inhibitor - benserazide (co-beneldopa, as Madopar) or carbidopa (co-careldopa, as Sinemet). The decarboxylase inhibitor reduces peripheral side-effects, principally nausea, of levodopa and its metabolites. Levodopa treatment is commenced (co-beneldopa 62.5 mg or co-careldopa 110 mg, one tablet three times daily) and gradually increased.

The great majority of patients with idiopathic PD (but not other parkinsonian syndromes) improve initially with levodopa. The response in severe, previously untreated idiopathic PD is sometimes dramatic.

Unwanted effects of levodopa therapy

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Nausea and vomiting are the most common immediate symptoms of excess levodopa. Confusion, formed visual pseudo-hallucinations and chorea also occur. There are difficult issues with long-term therapy (e.g. levodopa-induced involuntary movements). After several years levodopa gradually becomes ineffective, even with increasing doses. As treatment continues, episodes of immobility develop (freezing). Falls are common. Fluctuation in response to levodopa also appears, its effect apparently turning on and off, causing freezing alternating with dopa-induced dyskinesias, chorea and dystonic movements. Levodopa's duration of action shrinks, with dyskinesia becoming prominent several hours after a dose (end-of-dose dyskinesia). The patient also begins to suffer from a chronic levodopa-induced movement disorder.

Levodopa therapy does not alter the natural progression of idiopathic PD. After 5 years' treatment, around half of Parkinson's patients suffer from minor or major unwanted effects of therapy. The more distressing problems are often largely insoluble. Approaches to treatment of these complications include:

    * Shortening the interval between levodopa doses and increasing each dose.
    * Selegiline, a type B monoamine oxidase inhibitor, inhibits catabolism of dopamine in the brain. This sometimes smoothes out the response to levodopa.
    * Dopaminergic agonists (see below) are added, or replace levodopa.
    * Entacapone (a catechol-O-methyl transferase inhibitor) is used.
    * Drug holidays - periods of drug withdrawal - are occasionally helpful. They require close supervision since severe relapse may follow levodopa withdrawal.

Dopamine receptor agonists

Bromocriptine, lisuride, pergolide, cabergoline (ergot derivatives), pramipexole and ropinirole are oral directly acting dopamine receptor agonists, acting principally on D1 and D2 receptors, and also on receptors D3-5. These are used as an alternative or an addition to levodopa therapy. The ergot derivatives are associated with pulmonary, retroperitoneal and pericardial fibrotic reactions.

Apomorphine, a potent D1 and D2 agonist given by subcutaneous metered infusion is an effective method of smoothing out fluctuations in response to levodopa. Skilled nursing is required to train patients and relatives to set up the infusion pump. Vomiting is common. Haemolytic anaemia is an unusual side-effect.

Dopamine receptor agonists are in general less effective than levodopa in treating symptoms in Parkinson's disease, but cause fewer late unwanted dyskinesias.

There is much variation in clinical practice between different regimens of levodopa and dopamine receptor agonists. There is a trend towards the use of receptor agonists as primary treatment (before levodopa) and to delaying starting any drugs until it is clinically essential. Directly acting agonists are usually used below the age of 70, and levodopa for older cases.

Other agents

Antioxidant compounds such as vitamins C and E (possible neuroprotective agents) are sometimes suggested. Their role is uncertain. Amantadine, originally marketed as an antiviral drug, occasionally has a modest effect. Rivastigmine is helpful for the dementia.

Stereotactic neurosurgery

Stereotactic lesions, usually unilateral in the ventrolateral nucleus of the thalamus (thalamotomy) or in the globus pallidus (pallidotomy), were used widely before levodopa. Surgery still provides effective, if temporary improvement in tremor and dyskinesia with minor relief of bradykinesia. Thalamic stimulation is also used. There has been a revival of interest in surgery in the last decade.

Tissue transplantation

Despite early promise and suggestive laboratory studies in rats with MPTP-induced parkinsonism, tissue transplantation is little used. Experimental transplantation of fetal or autologous dopamine-containing adrenal medulla and glial cell-line neurotrophic releasing factor (GDNF) into the cerebral ventricles or basal ganglia, does not produce any sustained improvement.

Physiotherapy and physical aids

Skilled and determined therapy can improve gait and help overcome particular problems. Practical guidance is of value:

    * clothing - avoid zips, fiddly buttons and lace-up shoes
    * cutlery - use built-up handles
    * chairs - high upright rather than deep, low chairs
    * rails - near lavatory and bath
    * shoes - should be easy to put on and have smooth soles
    * flooring - vinyl is safer than loose carpets.

Walking aids are often a hindrance early on, but later a frame or a tripod may help. All efforts must be made to avoid falls.

Psychiatric aspects

Depression is common as PD progresses. Selective serotonin reuptake inhibitors (SSRIs) are the drugs of choice. Tricyclic antidepressants (e.g. amitriptyline) have extrapyramidal side-effects. Type A monoamine oxidase inhibitors (e.g. phenelzine) are absolutely contraindicated with levodopa.

All antiparkinsonian drugs can cause visual hallucinations, especially at night, and exacerbate cognitive impairment.

OTHER AKINETIC-RIGID SYNDROMES

Drug-induced parkinsonism

Reserpine and methyldopa (drugs once used to treat hypertension), phenothiazines and butyrophenones induce parkinsonism, with slowness and rigidity but usually little tremor. Tricyclic antidepressants also cause some slowing. These unwanted effects tend not to progress and settle when a drug is stopped. They respond negligibly to levodopa.

Neuroleptics and movement disorders

Neuroleptics (i.e. phenothiazines and butyrophenones) also produce movement disorders.

    * Akathisia. This is a restless, repetitive and irresistible need to move.
    * Acute dystonic reactions. These occur (dramatically and unpredictably) after single doses of neuroleptics and related drugs widely used as antiemetics and vestibular sedatives (e.g. metoclopramide and prochlorperazine). Spasmodic torticollis, trismus and oculogyric crises (i.e. episodes of sustained upward gaze) occur. These acute dystonias respond promptly to i.v. antimuscarinics, e.g. benzatropine (1-2 mg) or procyclidine 5-10 mg. The offending drug (and all similar) should be avoided forever.
    * Chronic tardive dyskinesias. These are mouthing and lip-smacking grimaces, disabling disorders that occur several years after commencing neuroleptics. They often become temporarily worse when the neuroleptic dose is reduced. Resolution seldom occurs, even if treatment ceases.

Post-encephalitic parkinsonism and MPTP (see p. 1228)

Parkinsonism-plus

This describes rare disorders in which there is parkinsonism with additional features and pathology. Progressive supranuclear palsy (Steele-Richardson-Olzewski syndrome) is the commonest. It consists of parkinsonism, axial rigidity, falls, dementia, and inability to move the eyes vertically or laterally. Other examples are multiple system atrophies, such as olivo-ponto-cerebellar degeneration and primary autonomic failure (Shy-Drager syndrome).

These are progressive, unresponsive to levodopa and usually cause death within a decade.

Akinetic-rigid syndromes in children

Several extremely rare disorders cause akinetic-rigid syndromes with onset under 20 years.

Wilson's disease

This rare but treatable disorder of copper metabolism is inherited as an autosomal recessive. Copper deposition occurs in the brain, particularly in the basal ganglia, in the cornea and liver (p. 387), where it causes cirrhosis. All young patients either with an akinetic-rigid syndrome or with cirrhosis should be screened for Wilson's disease. Neurological damage is reversible with early treatment. This akinetic-rigid syndrome and/or dyskinesias is followed by progressive intellectual impairment. Diagnosis and treatment with the chelating agent penicillamine is discussed on page 388.

Athetoid cerebral palsy

Writhing movements, sometimes with progressive dystonia, occur in cerebral palsy following kernicterus. This is now rare following prophylactic eradication of rhesus haemolytic disease with anti-D immunoglobulin.

DYSKINESIAS

Benign essential tremor

This common condition, often inherited as an autosomal dominant trait, causes 5-8 Hz tremor, usually worse in the upper limbs. The head is often tremulous (titubation) and also the trunk. Pathologically there is patchy neuronal loss in the cerebellum and its connections. Tremor develops when the hands adopt a posture, such as holding a glass or a spoon. Essential tremor occurs at any age but occurs most frequently in the elderly. It is slowly progressive but rarely produces severe disability. Writing is shaky and untidy: micrographia is absent. Anxiety exacerbates the tremor, sometimes dramatically. In essential tremor, shaking occasionally occurs at rest, as in Parkinson's disease, or on action, as in cerebellar disease.

Treatment is often unnecessary, and unsatisfactory. Many patients are reassured to find they do not have Parkinson's disease, with which essential tremor is often confused.

Small amounts of alcohol, β-adrenergic blockers (propranolol) and the anticonvulsant primidone may help the tremor: sympathomimetics (e.g. salbutamol) make it worse. The antidepressant mirtazapine has some effect. Stereotactic thalamotomy and thalamic stimulation are used in severe cases.

Chorea

Chorea means jerky, quasi-purposive, explosive, fidgety movements, flitting around the body - causes are listed in Table 21.40.

Huntington's disease

Table 21-40. Causes of chorea

Huntington's disease

Sydenham's chorea

Benign hereditary chorea

Abetalipoproteinaemia (see p. 308) with chorea

Chorea associated with:

 Drugs - phenytoin, levodopa, alcohol

 Thyrotoxicosis, pregnancy and oral contraceptive pill

 Systemic lupus erythematosus

 Polycythaemia vera

 Encephalitis lethargica

 Stroke (basal ganglia)

 Rarities (tumour, trauma, subdural haematoma, following carbon monoxide poisoning, paroxysmal choreoathetosis, Wilson's disease, dentato-rubro-pallido-luysian atrophy)


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Relentlessly progressive chorea and dementia, usually in middle life but sometimes in childhood, are hallmarks of this inherited disease. Prevalence world-wide is about 5 in 100 000. Inheritance is as an autosomal dominant trait with full penetrance: children of an affected parent have a 50% chance of developing Huntington's disease. Previous family history is often concealed, sometimes deliberately. A mutation occurs in the distal short arm of chromosome 4 (4p16.3) with a variable expansion of a CAG-repeat sequence located in exon 1 of a large gene containing 67 exons. This results in translation of an extended glutamine sequence in huntingtin, the protein product of the gene. Huntingtin is expressed throughout the body. Its function is unclear. Most adult-onset HD cases have CAG expansions of 40-55 repeats, while greater expansions (>70 repeats) are seen in childhood-onset HD.

Pathology

Cerebral atrophy progresses, with marked loss of small neurones in the caudate nucleus and putamen.

Changes in neurotransmitters occur:

    * reduced acetylcholine synthesis (due to reduced choline acetyl transferase) and GABA in the striatum
    * increased transglutaminase (catalyses aggregates of huntingtin) in cortex, cerebellum and corpus striatum
    * depleted GABA, angiotensin-converting enzyme and met-enkephalin in substantia nigra
    * high somatostatin levels in the corpus striatum.

These may be secondary to cell damage. In contrast to Parkinson's disease, dopamine and tyrosine hydroxylase remain normal.

Management and course

Other causes of chorea should be investigated. Imaging in Huntington's, if practical with the chorea, shows caudate nucleus atrophy. There is steady progression, of both dementia and chorea. While nothing arrests this, phenothiazines (e.g. sulpiride) and tetrabenazine reduce chorea. Death usually occurs 10-20 years from the onset.

Mutation analysis is used for presymptomatic testing. Test centres have a national protocol for counselling families and addressing the ethical issues.

Sydenham's chorea (St Vitus's dance)

This transient postinfective chorea occurs largely in children and young adults. Streptococcal infection is one cause: under half the cases follow within 3 months of rheumatic fever (p. 76). Sydenham's may recur, or appear, in adult life, during pregnancy as chorea gravidarum and with hormonal contraceptives. There is a diffuse mild encephalitis.

The onset is gradual over a few weeks. Irritability, emotional lability, and inattentiveness herald fidgetiness, sometimes mainly unilateral. A minority of patients become confused. Rheumatic heart disease is sometimes found. Fever is unusual. Antistreptolysin-O (ASO) titre and ESR are typically normal. Sedation may be needed. Recovery occurs spontaneously within weeks or months. Phenoxymethylpenicillin should continue to the age of 20 to prevent rheumatic heart disease.

Hemiballismus (see p. 1194 and Fig. 21.9)

Hemiballismus (also called hemiballism) describes violent swinging movements of one side caused usually by infarction or haemorrhage in the contralateral subthalamic nucleus.

Myoclonus

Myoclonus is sudden, involuntary jerking of a single muscle or a group of muscles. It occurs in a wide range of disorders and is sometimes provoked by sudden stimuli such as loud noise. Piracetam is used for cortical myoclonus.

Benign essential myoclonus

Nocturnal myoclonus - sudden jerking (often with a feeling of falling) on dropping off to sleep - is common and not pathological. Periodic limb movements (repetitive dorsiflexion of the great toe or plantar flexion of the foot during Stage I or II sleep) are brief and occur in restless leg syndrome (p. 666).

Paramyoclonus multiplex describes widespread, random muscle jerking usually occurring in adolescence. Fits do not occur.

Myoclonus in epilepsy

Muscle jerking occurs in many different forms of epilepsy. An antiepileptic drug, e.g. valproate, may be helpful.

Progressive myoclonic epilepsies

These rare conditions include familial and metabolic disorders where myoclonus accompanies progressive encephalopathy. Lafora body disease is one example, consisting of myoclonus, epilepsy, dementia, with mucopolysaccharide inclusions in neurones, liver cells and intestinal mucosa.

Static myoclonic encephalopathy

Non-progressive myoclonus sometimes develops following recovery from severe cerebral anoxia.

Non-organic muscle jerking.

This is sometimes volitional, or seen in psychiatric conditions, e.g. somatization, non-epileptic attacks and malingering.

Tics

Some idiosyncratic movement of the face, neck or hand is part of our normal motor gestures. Patients or relatives seek advice when movements become frequent or irritating. Simple transient tics (e.g. sniffing or a particular facial grimace) are common in childhood, but may persist. The borderland between normal and pathological is vague.

Gilles de la Tourette syndrome

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Table 21-41. A classification of dystonias

    * Generalized dystonia Primary torsion dystonia (PTD)
    * Dopamine-responsive dystonia (DRD)
    * Drug-induced dystonia (e.g. metoclopramide)
    * Symptomatic dystonia (e.g. after encephalitis lethargica or in Wilson's disease)
    * Paroxysmal dystonia (very rare, familial, with marked fluctuation)

    * Focal dystonia Spasmodic torticollis
    * Writer's cramp
    * Oromandibular dystonia
    * Blepharospasm
    * Hemiplegic dystonia (e.g. following stroke)
    * Multiple sclerosis


This describes multiple tics (motor and speech) with behavioural problems including the attention-deficit-hyperactivity disorder (ADHD) and the obsessive-compulsive disorder (OCD). This develops in childhood or adolescence, more commonly in males, and is lifelong. There is sometimes explosive barking and grunting of obscenities and gestures. The cause is believed to be an inherited disorder of synaptic transmission. Haloperidol is sometimes helpful.

Torsion dystonias

Dystonia means movement caused by prolonged muscular contraction - part of the body is thrown into spasm. A brief explanatory classification of these unusual basal ganglia conditions is given in Table 21.41. Their causes are largely unknown.

Primary torsion dystonia (dystonia musculorum deformans)

Dystonia affecting gait and posture in childhood progresses, spreading to all parts of the body over one to four decades. Cognitive function is not impaired. Spontaneous remissions occur occasionally. This rare disease is usually inherited as an autosomal dominant. A PTD gene has been located on chromosome 9 (9q34); this is a deletion of three base pairs encoding an ATP-binding protein torsin A.

Dopamine-responsive dystonia (DRD)

This lower limb dystonia is almost completely abolished by small doses of levodopa. Typically dystonic walking begins in childhood - and may resemble a spastic paraparesis. The usual form is autosomal dominant DRD with a point mutation of the GTP cyclohydrolase 1 gene on chromosome 14q22.3. Patients with other odd dystonic gaits are sometimes given test doses of levodopa.

Spasmodic torticollis

Dystonic spasms gradually develop around the neck, usually in the third to fifth decade. These cause the head to turn (torticollis) or to be drawn backwards (retrocollis) or forwards (antecollis). Minor dystonic movements often also affect the trunk and limbs. A curious feature in some patients is a single trigger area, often on the jaw. A gentle touch with a finger tip at this specific site relieves the spasm temporarily. Torticollis may remit but often persists indefinitely. Similar features are sometimes seen when no organic disease is present.

Writer's cramp

This is a specific inability to perform a previously highly developed repetitive skilled movement, e.g. writing. The movement provokes dystonic posturing. Writer's cramp occurs in those who spend many hours each day writing, and is thus seen less frequently than in years past. Other functions of the hand remain normal. There are no other neurological signs. Prolonged rest sometimes helps but the dystonia can cause substantial disability. Similar dystonias occur in other occupations.

Blepharospasm and oromandibular dystonia

These consist of spasms of forced blinking or involuntary movement of the mouth and tongue (e.g. lip-smacking and protrusion of the tongue and jaw). Speech may be affected.

Treatment

All dystonic movement disorders are particularly difficult to help. Butyrophenones (e.g. haloperidol and sulpiride) and antimuscarinics (e.g. trihexyphenidyl (benzhexol)) are sometimes helpful. Botulinum toxin carefully sited by injection can help, temporarily, blepharospasm, torticollis and writer's cramp. Neurosurgical treatment, principally stereotactic thalamotomy for torticollis, or neurostimulation brings some temporary alleviation in selected cases.

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