Summary Ataxias arise from dysfunction of the cerebellum or its connections, causing disordered and irregular movement. There are several different hyperkinetic movement disorders, which are distinguished by clinical evaluation: in chorea , involuntary movements are random; In dystonia , the movements have a pattern; in tremor , the movements are rhythmic; In myoclonus , movements are very brief, jerky and irregular; and in tics , the movements are suppressible and are associated with an underlying sense of urgency. This article provides an approach to the diagnosis of patients with ataxic and hyperkinetic movement disorders and discusses some common and important diagnostic associations. Explores the generalities of treatment that includes the use of deep brain stimulation, effective in correctly selected patients. |
Hyperkinetic movement disorders are a heterogeneous collection of disorders that cause involuntary movements. Observation of the patient and recognition of the movement pattern can diagnose most hyperkinetic movement disorders, and much of this can be done while taking the history. Table 1 illustrates the tips for the exam.
| Ataxia |
> Definition
The cerebellum tunes and coordinates movement. Ataxic patients report clumsiness in attempts to move, poor balance, and difficulty speaking. Ataxia can be cerebellar or sensory (caused by disorders of proprioception, including sensory neuropathy).
> Ataxia tests
• Eye movements : Pursuit eye movements (following a finger) are often jerky in ataxic patients. Saccadic eye movements (looking from one target to another) often overshoot the target. Nystagmus may be seen.
• Speech : Patients with ataxia often have dysarthria . Cerebellar dysarthria is irregular or has explosive speech or unnaturally separated syllables ("scanning dysarthria"). It can be difficult to distinguish from other forms of dysarthria.
• Upper limbs : the finger/nose test is used. The patient reaches out to touch the examiner’s finger, then flexes his arm to touch his nose with the tip of his finger. The process is repeated. The examiner looks for poorly coordinated movements that overshoot or miss the target; sometimes a tremor develops as the target is approached (intention tremor). The patient should fully straighten the arm, as subtle ataxia only develops when the arm is extended to get closer to the target. In cases of severe incoordination, it is safer to ask the patient to touch their chin to avoid injury.
Rapid alternating motion disorder ( dysdiadochokinesia ) is tested by asking the patient to alternately pronate and supinate the hand while tapping the thigh with it. Ataxic patients demonstrate loss of rhythm and fragmentation of movements during this test.
• Lower extremities : Ataxia is tested using the heel shin test, looking for the loss of soft contact of the heel when lowered along the contralateral shin.
• Gait : An ataxic gait is broad-based and unstable. Patients struggle with tandem walking (where the heel of the front foot touches the toes of the back foot with each step).
• Sensory ataxia : Patients with sensory rather than cerebellar ataxia have reduced proprioception and instability of outstretched hands with eyes closed. They are also unstable when standing still with eyes closed and feet together (Romberg test).
Examination of a patient with a hyperkinetic movement disorder
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> Causes of ataxia (Table 2)
Cerebellar disorders can be acute (seconds, minutes, hours), subacute (days, weeks), or chronic (months, years). Toxic causes such as alcohol are determined from history. Acute onset (for a few seconds) raises suspicion of vascular injury (stroke), and subacute onset (for days or a few weeks) suggests a demyelinating-inflammatory or infectious etiology. Structural problems show up on cranial MRI.
Age of onset is a clue in chronic cerebellar disorders. Many genetic disorders present at a younger age, with multiple sclerosis prevalent in adults, while degenerative causes, such as multiple system atrophy, present at an older age.
Imaging helps differentiate chronic disorders: Some conditions (eg, ataxia telangiectasia, most spinocerebellar-dominant ataxias) cause cerebellar atrophy, while others (eg, Friedreich’s ataxia) do not . Disorders of the cerebellum are discussed in more detail elsewhere.
Table 2 Important causes of ataxia Immediate start
Start in days
Start for weeks or months
Home over the years
Non-cerebellar causes
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| Korea |
> Definition
Chorea denotes random involuntary movements, which usually affect the entire body. A patient with chorea may simply appear restless, and sometimes it is difficult to distinguish anxious, restless movements from chorea. A restless patient is usually able to suppress movements when concentrating on tasks such as writing, while chorea worsens with action and writing may be difficult. Motor impermanence tests often help (Table 1).
> Causes
Medical causes: include nonketotic hyperglycemia, hyperthyroidism, systemic lupus erythematosus, antiphospholipid syndrome and polycythemia, Sydenham’s chorea (poststreptococcal), and chorea during pregnancy (chorea gravidarum). Medications, including levodopa, the oral contraceptive pill, anticholinergic drugs, anticonvulsants, and antidepressants, can cause chorea.
A stroke in the basal ganglia can produce contralateral hemichorea; Involuntary movements can be large-amplitude, dramatic, forceful throwing movements of an entire extremity (ballistic movements).
• Huntington’s disease : This autosomal dominant condition is caused by an expanded trinucleotide repeat in the huntingtin gene on chromosome 4. It presents with a premotor neuropsychiatric syndrome (depression, personality change), cognitive problems, and later a disorder of movement (usually chorea but sometimes dystonia or parkinsonism).
• Other causes : Neurodegeneration with iron accumulation in the brain, as well as several other genetic conditions, including mutations in ADCY5, NKX2-1, and C9orf72.
| Dystonia |
> Definition
In dystonia, sustained muscle contractions cause twisting movements and abnormal postures. While chorea causes random movements, dystonia causes patterned movements, that is, the same movement is performed over and over again. For example, if the head turns to the left (torticollis), it repeatedly turns to the left. Dystonia is focal when it only affects one part of the body, for example, the neck (cervical dystonia), the eyes (blepharospasm), or the extremities. It can be segmental (for example, affecting the face and neck) or generalized, when the entire body is affected.
> Types
• Task-specific dystonia – This occurs only with certain activity, such as writing (writer’s cramp). This is particularly common in people who write a lot and find their fingers or arms adopt an unusual posture, making writing difficult. Other highly learned complex activities may be associated with task-specific dystonia, including gaming, playing a musical instrument, and certain sports (for example, the ’yips’ in golf).
• Primary torsion dystonia : usually genetic. Patients are neurologically normal apart from dystonia (and sometimes tremor). Some of the genes involved have been characterized. When it begins in childhood , it usually presents as lower limb dystonia, gradually progressing to generalized dystonia. Adults commonly present with focal dystonia, particularly cervical dystonia and blepharospasm.
• Cerebral palsy : Dystonia is usually generalized and caused by perinatal brain injury such as neonatal jaundice ("kernicterus") or hypoxic brain injury.
• Dopa-responsive dystonia – These genetic conditions often present with childhood dystonia that mimics dystonic cerebral palsy. Patients respond dramatically to levodopa and go from needing a wheelchair to normal mobility. Although rare, this condition should not be overlooked , and all patients with possible dystonic cerebral palsy should have a trial of levodopa (co-careldopa 125 mg three times a day for 2 weeks).
• Wilson’s disease : this is an autosomal recessive defect in copper metabolism. It presents with liver disease or neurological problems, including personality change, dystonia, and tremor. A typical dystonic facial posture can cause a "smiling" expression and difficulties eating or speaking. Most patients have a copper ring around the cornea visible on slit-lamp examination (Kaysere-Fleischer ring), low serum ceruloplasmin concentration, and high urinary copper excretion. Early diagnosis and treatment prevents permanent disability.
• Other causes : include medications (L-dopa, neuroleptics), vascular causes, and acquired brain damage. Rare causes of dystonia include neuroacanthocytosis and neurodegeneration with iron accumulation in the brain.
| Tremor |
> Definition
Tremor is a rhythmic oscillation over a part of the body. It can affect any part of the body, most commonly the arms. The nature of the tremor, particularly whether it is a resting tremor or a postural and action tremor, provides an important clue to the diagnosis.
Rest- predominant tremors are usually caused by Parkinson’s disease. Parkinsonian tremor can sometimes occur with sustained posture, but there is usually a delay between the arms being extended and the tremor developing or becoming more pronounced (this tremor is called reemerging postural tremor ). An action tremor occasionally occurs in Parkinson’s disease.
> Causes
• Medical causes : Everyone has a high-frequency physiological tremor that becomes more evident with stress. Hyperthyroidism and drugs (including β-adrenoceptor agonists, lithium, and sodium valproate) cause or worsen tremor, and special attention should be paid to drug history.
• Essential tremor : causes a postural and action tremor with a frequency slightly lower than the physiological tremor. Unlike a parkinsonian reemerging tremor, essential tremor occurs immediately in a sustained posture. The tremor worsens with action (which is unusual for parkinsonian tremor). A typical patient with parkinsonian tremor might complain that her tremor was worse when watching television, while patients with essential tremor usually complain of difficulty holding a cup of tea.
Essential tremor is usually familial , although the causative genes are unknown. When associated with dystonia, the term " dystonic tremor " may be more appropriate to describe it. Although often called " benign ," essential tremor can be very disabling.
• Other causes : There are many other causes, including Holmes tremor (rubral or midbrain tremor), cerebellar tremor, and orthostatic tremor (high-frequency tremor of the legs when standing).
| Myoclonus |
> Definition
Myoclonus refers to very brief muscle twitches. It can affect the entire body at once (generalized myoclonus) or a small area such as the fingers (focal myoclonus). Myoclonus can be positive (jerks are brief muscle contractions) or negative (jerks are caused by a brief loss of sustained muscle contraction).
> Causes
A large number of conditions cause myoclonus, and the diagnosis is usually made by recognizing characteristics of these conditions other than the myoclonus itself.
•Medical causes : Several medical conditions can cause myoclonus. The metabolic flap of outstretched arms seen in respiratory, hepatic, and renal failure is a form of negative myoclonus ( asterixis ). Medications , including opioids and gabapentin, can also cause myoclonus .
• Neurological causes : Myoclonus can originate at any level of the central nervous system, including the cortex, subcortical regions, and spinal cord. Neurological conditions that cause myoclonus include several epileptic disorders, Alzheimer’s disease, cortical Lewy body disease, CreutzfeldteJacob disease, and posthypoxic myoclonus. Other rare genetic causes include myoclonodystonia syndrome.
| Tics |
> Definition
A tic is a semi-involuntary movement made in response to an internal impulse (in the same way that an itchy sensation triggers the desire to scratch). Tics can usually be suppressed for a short period if the patient is asked to do so, but the internal drive “builds up” and tics worsen when patients stop trying to suppress them. Tics can affect any part of the body, although blinking, raised eyebrows, and shoulder movements are common. These motor tics can be confused with other movement disorders unless you ask the patient about the internal drive and try to see if he or she can suppress the movements. In addition to these motor tics, vocal tics, such as throat clearing, are common. Swearing (coprolalia) may occur, but is less common.
> Causes
Tics are common, affecting more than 10% in childhood and adolescence. They usually improve after adolescence, but occasionally worsen in adulthood. Tourette syndrome is a severe tic disorder, often accompanied by obsessive-compulsive disorder and attention deficit hyperactivity disorder. Tic disorder also occurs in other neurological conditions, including Huntington’s disease.
| tardive dyskinesia |
Long-term treatment with dopamine receptor blocking medications can cause involuntary movements called tardive dyskinesia . The drugs most frequently implicated are neuroleptics, including haloperidol and chlorpromazine. The dopamine-blocking anti-nausea medications prochlorperazine and metoclopramide also cause tardive dyskinesia.
The most common manifestations of tardive dyskinesia are repetitive orolingual movements that are reduced when the patient speaks or eats. Virtually any movement disorder can be late-onset (i.e., caused by long-term treatment with dopamine blockers), including dystonia, tremor, and an internal restlessness called akathisia .
> Functional movement disorders
Many of the movement disorders mentioned above may have functional or psychogenic causes and comprise at least 5% of referrals to a movement disorder clinic.
Distinguishing a functional movement disorder from an organic one can be difficult. It is important to look for incongruence (the movement disorder is not typical of a known movement disorder) and inconsistency (the movement disorder changes over time). Unlike organic movement disorders, which worsen with distraction , most functional movement disorders improve with distraction . Dragging is common in functional tremor (see Table 1).
> Generalities of the treatment of movement disorders.
Some ataxias are treated by addressing the underlying cause, for example, giving thiamine for Wernicke encephalopathy or immunotherapy for autoimmune ataxia. Apart from this, the pharmacological treatment of ataxias is disappointing. Botulinum toxin injections are effective in the treatment of focal dystonia, for which they are the first-line treatment, and may be useful for some focal tics. Medications used to treat hyperkinetic movement disorders often have bothersome adverse effects and many patients prefer to avoid them. In more severe cases, deep brain stimulation can be extremely effective in the correctly chosen patient.
