MOVEMENT DISORDERS

The term Movement disorders refers to many transient or persistent and pathological or psychological disorders, characterized by abnormal movements and/ or posturing of all or parts of body (excluding seizures).

Movement disorders are classified as hyperkinetic or hypokinetic. Hyperkinetic disorders include ataxia, chorea, athetosis, tremors, myoclonus and tics. Hypokinetic disorders with paucity of movements are rare in children and include juvenile parkinsonism. Many movement disorders may co-exist in the same patient.

Ataxia denotes ‘inability to sustain a posture or perform smooth and accurate movements due to lack of coordination between different groups of muscles'.

Ataxia may be (a) truncal (abnormality in maintaining the erect posture), (b) appendicular affecting the limbs (difficulty in performance of certain coordinated acts), or (c) mixed.

Etiologically, Fine control of posture and movements requires normal positional sensory inputs from posterior spinal columns and vestibular system as well as normal cerebellar functions. Accordingly, ataxia may be cere­bellar, sensory or vestibular in origin (Table 18.23). Isolated truncal ataxia is common in mid-line cerebellar lesions while isolated appendicular ataxia is seen in lesions of cerebellar hemispheres.

In children, Acute cerebellar ataxia following viral infections and drugs, e.g. anticonvulsants is most common.

TABLE 18.23: Causes of ataxia in children

A. Cerebellar ataxia

• Acute cerebellar ataxia (Post-infectious cerebellitis)

• Ataxic cerebral palsy

• Infections: Encephalitis, cerebellar abscess

• Congenital cerebellar malformations, hydrocephalus

• Toxic: Alcohol, anticonvulsants*, pesticides

• ICSOL: Tumors, tuberculoma, neurocysticercosis

• Hereditary: Ataxia telangiectasia, Friedreich's ataxia

• Metabolic:

- Hypoglycemia, hyperammonemia

- IEMs: Wilson disease, abetalipoproteinemia

• Others: Post-ictal, post-traumatic, basilar migraine

B.

• Polyneuropathies

• Intramedullary spinal tumors

• Subacute combined degeneration of spinal cord

C. Vestibular Ataxia

• Acute labyrinthitis

• Middle ear disorders,

• Benign paroxysmal vertigo

ICSOL: Intracranial space occupying lesion; IEM: Inborn errors of metabolism

*e.g. Phenytoin, Carbamazepine.

Clinically, Ataxia may be acute or persistent and important clinical signs include:

• Abnormal gait (Wide-base gait) and inability to walk in a straight line (Tandem walking). While walking or standing, child tends to sway towards the side of cerebellar lesion. Children with sensory ataxia usually have stamping gait, due to difficulty in assessing the distance from ground.

• Impaired coordination, as assessed by Finger-nose test or Heel-to-shin test, even with open eyes.

• Romberg sign, i.e. failure to stand erect steadily with outstretched hands, helps to distinguish cerebellar from sensory ataxia. Inability to maintain normal posture even with open eyes indicates cerebellar ataxia.

• Other cerebellar signs, e.g. dysdiadochokinesia, nystagmus, dysarthria, pendular jerks and hypotonia indicate cerebellar ataxia.

• Vestibular ataxia is associated with vertigo and nystagmus.

Evaluation: Most cases of ataxia are viral and self­limiting. However, neuroimaging studies are indicated in cases with—(a) progressive or persistent ataxia gt;1 week and, (b) presence of other neurological signs. MRI is preferable in ataxic children, as infratentorial cerebellar lesions are not well visualized on CT scan.

Management include treatment of primary cause, though most cases in children are due to self-limiting post-viral acute cerebellar ataxia.

Some common causes of ataxia are as follows:

Acute cerebellar ataxia following viral infections, e.g. varicella, coxsackievirus or echovirus infection is the commonest cause of ataxia in children between 1-5 years of age. Ataxia may develop within a few hours of viral illness and usually self-limiting with complete recovery within 3-7 days.

Recurrent ataxia with intervening normal period is seen in: (a) basilar artery migraine (Benign paroxysmal vertigo, Ch 18.6.5), (b) epileptic disorders (during post-ictal state), and (c) inborn errors of metabolism, e.g. hypoglycemia, hyperammonemia and ion channel mutations, e.g. KCNA1.

Hysterical ataxia is a conversion reaction more common in adolescent girls to cope with a stress or for some secondary gain, though many events are involun­tary. Unlike organic ataxia, these children usually do not injure themselves and diagnosis depends on discrete observation.

Dystonia refers to slow, intermittent and sustained twisting motion of the trunks and limbs with development of abnormal postures, due to sustained contraction of agonists and antagonists group of muscles. Dystonia may be painful and aggravate during stress or voluntary activity.

Etiologically, Dystonia may be isolated or secondary.

Isolated dystonia without other motor components is almost always genetic in origin, commonest being DYT-TOR1 dystonia with onset in late childhood or adolescence.

Secondary or combined dystonia with other motor components may be due to: (a) cerebral palsy, (b) juvenile parkinsonism, (c) drugs, e.g. phenytoin, phenothiazines, metoclopramide, (d) metabolic disorders, e.g. Wilson disease, and (e) neurotransmitter disorders.

Clinically, Acute-onset dystonia is usually secondary to drugs, while dystonia due to genetic causes is usually paroxysmal in nature with recurrent history and normal intervening period.

Status dystonicus is a life-threatening condition, with frequent or continuous generalized dystonic spasms, common in cerebral palsy or neurodegenerative dis­orders, often precipitated by fever or other stressors.

Diagnosis needs assessment for age of onset, distribution (focal/generalized), progression (static/progressive) and presence of other neurological and systemic abnormalities, followed by ophthalmic examination (KF ring, retinitis pigmentosa) and MRI (essentially normal in primary DYT dystonia) in all cases and metabolic screening or genetic studies in selected cases.

Management include treatment of primary cause, if identified, along with symptomatic therapy with therapeutic trial of levodopa in all dystonic children. However, the response is variable and often unsatisfactory. Neurosurgical procedures, e.g. deep brain stimulation may help in refractory cases.

Status dystonicus needs careful use of sedatives including chloral hydrate (PO 30-100 mg/kg/dose 3-4 hourly) with/without clonidine (3-5 #956;g#8725;kg#8725;dose

6-8 hrly). Continuous midazolam infusion may also be effective. Dystonia-specific drugs, e.g. Trihexyphenidyl (Pacitane) or Tetrabenazine, etc. may be required on long-term basis.

Chorea is defined as involuntary quick, random, jerky movements of skeletal muscles, mainly at the proximal joints, e.g. shoulder, etc. Hemichorea is the unilateral variant. Motor impersistence, i.e. inability to maintain sustained posture makes the child appears fidgety or hyperactive. Important clinical signs of chorea include: (a) inability to keep the arms when extended above the head with palms facing inward, (b) inability to keep tongue protruded, i.e. Lizard tongue, darting tongue or tongue in jack box appearance, and (c) inability to sustain the grip over examiner's finger, i.e. milkmaid's grip (Ch 17.6).

Etiologically, Important causes of chorea include: (a) Sydenham or rheumatic chorea, (b) Huntington or familial chorea, (c) drugs, e.g. phenytoin, amitripty­line, etc., (d) Wilson disease, and (e) others, e.g. SLE, hyperthyroidism, hypoparathyroidism. Among these, rheumatic chorea is the commonest cause of chorea in children (Ch 17.6), followed by Wilson disease.

Choreiform movements may also be seen during recovery phase of tubercular meningitis or encephalitis, along with other abnormal movements, e.g. athetosis.

Management: Antipsychotic agents like olanzapine or risperidone may be useful for symptomatic control of acute onset chorea with alternatives including Tetrabenazine and anti-epileptics like valproic acid or carbamazepine.

Rheumatic (Sydenham) chorea is the commonest cause of chorea in Indian children, discussed in Ch 17.6.

Benign hereditary chorea is a rare autosomal dominant disorder with onset at 2-5 years of age and improvement in adulthood. Intelligence is normal Huntington chorea (autosomal dominant) is a progressive NDD of middle­age adults with predominant basal ganglia involvement. Less that 1% cases present in childhood with progressive rigidity, dystonia, chorea, dementia and seizures. Diagnosis is clinical, though CT may show basal ganglia atrophy. Management is nonspecific and most cases die within 10-15 years.

Ballismus and hemiballismus, i.e. frequent, violent, rapid, flinging movements of proximal joints of one or both arms, usually indicates vascular or neoplastic lesions near the sub-thalamic nuclei. It is uncommon in children.

Athetosis presents as irregular, often continuous, slow writhing movements of the extremities, mainly in distal parts, e.g. alternate pronation and supination of wrists. Common causes include: (a) cerebral palsy, (b) cerebral hypoxia, (c) meningitis, (d) hypothermia and (e) drugs, e.g. phenothiazines.

Stereotypic movement disorders: Stereotypies are repetitive, non-functional, patterned movements and/ or vocalizations, which can be suppressed by distraction. Simple stereotypies like leg-shaking, body-rocking etc are common in normal children, which disappear with time. Complex stereotypies like hand-flapping, oro­facial movement and eye-poking, which interfere with functions or may be self-injurious, are abnormal.

Complex stereotypies are usually associated with Rett syndrome, autism, intellectual disability and in children with vision or hearing impairment. Treatment of primary disease along with behavioral therapy may be useful in these cases.

Tics are sudden, brief, purposeless, stereotyped movements, which are exacerbated in stress and dis­appear during sleep. While habit tics are common in most children, persistent and debilitating tics suggest possibility of Tourette syndrome (Ch 5.5.4).

Tremors are prolonged or continuous involuntary rhythmic movements of usually distal parts, e.g. fingers, which may be coarse or fine. Tremors are best demonstrated on outstretched hands and usually tend to diminish during sleep. Jitteriness in newborns is also a type of tremor. Tremors are also classified as resting tremors or action tremors.

Transient tremors in older children are commonly seen during salbutamol therapy. Other causes of tremors include: (a) essential or idiopathic tremors, (b) infantile tremor syndrome, (c) drugs, e.g. salbutamol, aminophylline or substance abuse, (d) metabolic disorders, e.g. acute hepatic failure, Wilson disease, hypoglycemia, and

(e) others, e.g. thyrotoxicosis or neuroblastoma.

Infantile Tremor Syndrome

Infantile tremor syndrome (ITS) is characterized by a clinical tetrad of—(a) tremors, (b) developmental regression,

(c) moderate anemia of usually megaloblastic type, and (d) hyperpigmentation of skin. ITS is largely confined to Indian subcontinent and the incidence has declined in recent years.

Epidemiology: ITS is typically seen in children between 6 months to 3 years, more common in: (a) boys, (b) low socioeconomic status, (c) fullterm birth, (d) prolonged breastfeeding, (e) second or subsequent birth order, and

(f) summer season (April to July).

Etiopathogenesis is unexplained, though various sug­gestions include: (a) nutritional recovery syndrome similar to that in malnutrition with relative GABA deficiency, (b) vitamin B₁₂ deficiency, (c) trace-element deficiency, e.g. hypomagnesemia or hypozincemia,

(d) low-grade meningoencephalitis, (e) transient meta­bolic defect in tyrosine metabolism, and (f) toxic insult to growing brain due to some unidentified toxin in breast milk.

Clinically, ITS may be divided into three stages:

a. Pre-tremor phase, characterized by developmental regression in a previously normal child, lasting from few days to many weeks.

b. Tremor phase, often preceded by stress factors, e.g. respiratory infection or diarrhea, is characterized by:

- Neurological signs including: (a) abrupt onset of generalized coarse tremors, most prominent in hands, head and tongue, which intensify during activity and disappear on sleep, (b) generalized hypotonia, (c) vacant and expressionless face, (d) side to side tossing movements of head, and (e) typical tremulous cry like bleating of a goat

- Mild to moderate anemia, often megaloblastic or dimorphic type.

- Dark-brown hyperpigmentation of skin, mainly on the dorsum of hands/feet, groin, medial side of thigh and axilla. Hairs are often light-brown, sparse and lusterless, as seen in kwashiorkor.

Tremor phase is self-limiting, with abrupt cessa­tion of tremors after few weeks (usually 2-3 week).

c. Post-tremor phase denotes convalescence with regaining of milestones and disappearance of skin signs in next few weeks. Although long-term cognitive dysfunctions have been reported, mortality is almost nil due to ITS.

Diagnosis is largely clinical, supported by presence of megaloblastic/dimorphic anemia and normal CSF.

Transient, non-specific EEG abnormalities are common. CT/MRI may reveal ventricular dilatation in some cases.

Management is empirical, including-(a) correction of megaloblastic anemia with Vitamin B₁₂ and folic acid supplements, (b) mild sedation with phenobarbitone or chlorpromazine in severe tremors, and (c) nutritional supplementation. Unexplained improvement has been claimed with oral propranolol or emetine therapy.

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