Voluntary movement requires interaction of the corticospinal (pyramidal) tracts, basal ganglia, and cerebellum (the center for motor coordination). The pyramidal tracts pass through the medullary pyramids to connect the cerebral cortex to lower motor centers of the brain stem and spinal cord. The basal ganglia (caudate nucleus, putamen, globus pallidus, subthalamic nucleus, and substantia nigra) form the extrapyramidal system. They are located deep in the forebrain and direct their output mainly rostrally through the thalamus to the cerebral cortex. Most neural lesions that cause movement disorders occur in the extrapyramidal system; thus, movement disorders are also called extrapyramidal disorders.
Movement disorders are classified as those with decreased or slow purposeful movements (hypokinesia) or those with excessive voluntary or abnormal involuntary movements (hyperkinesia). Although disorders of the cerebellum also impair gait and movement, they are classified separately (see Movement and Cerebellar Disorders: Cerebellar Disorders).
Hypokinesia: Most hypokinetic disorders are parkinsonian disorders, which are characterized by slow and decreased movement, muscular rigidity, resting tremor, and postural instability (see Movement and Cerebellar Disorders: Parkinson’s Disease).
Hyperkinesia: There are many hyperkinetic disorders (Fig. 1: Movement and Cerebellar Disorders: Classification of hyperkinesias. and Table 1: Movement and Cerebellar Disorders: Hyperkinetic Disorders). They can be subclassified as rhythmic or nonrhythmic.
Classification of hyperkinesias.
Rhythmic disorders are primarily tremors—regular alternating or oscillatory movements, which can occur mainly at rest (as resting tremor) or during attempted movement (as intention tremor).
Nonrhythmic disorders are characterized as slow (eg, athetosis), sustained (eg, dystonias), or rapid. Rapid disorders are characterized as suppressible (eg, tics) or nonsuppressible (eg, hemiballismus, chorea, myoclonus). Athetosis and chorea often occur together as choreoathetosis. Chorea occurs in Huntington’s disease (see Movement and Cerebellar Disorders: Huntington’s Disease). Tic disorders include Tourette’s syndrome (see Neurologic Disorders in Children: Tourette’s Syndrome).
Huntington’s disease, encephalitis, hepatic encephalopathy
Drugs (eg, cocaine, amphetamines, antipsychotics)
Movements are nonrhythmic, slow, writhing, sinuous, primarily in distal muscles; alternating postures of the proximal limbs often blend continuously to produce a flowing stream of movement.
Athetosis often occurs with chorea as choreoathetosis.
Huntington’s disease, thyrotoxicosis, paraneoplastic syndromes, SLE affecting the CNS, other autoimmune disorders, rheumatic fever, tumors or infarcts of the caudate nucleus
Pregnancy, often in women who had rheumatic fever
Age > 60 (as senile chorea)
Drugs (eg, antipsychotics)
Movements are nonrhythmic, jerky, rapid, and nonsuppressible, primarily in distal muscles or the face.
Sometimes abnormal movements merge imperceptibly into purposeful or semipurposeful acts that mask the involuntary movements.
Chorea often occurs with athetosis.
Drugs, most often antipsychotics (eg, phenothiazines, thioxanthenes, butyrophenones) or antiemetics
Nonrhythmic sustained muscle contractions occur, often distorting body posture.
Usually, damage to the subthalamic nucleus or nuclei due to hemorrhagic or ischemic strokes, metastatic tumors, cysts, infectious disorders, or inadvertent tissue damage during neurosurgery
Movements are nonrhythmic, rapid, nonsuppressible, violent, and flinging; they occur unilaterally, primarily in the proximal arm.
See Table 2: Movement and Cerebellar Disorders: Causes of Myoclonus.
Nonrhythmic, rapid, nonsuppressible, shocklike twitches occur, sometimes in multiple muscles simultaneously.
Tourette’s syndrome, Huntington’s disease, primary dystonia, neuroacanthocytosis, Hallervorden-Spatz disease, infections, stroke, obsessive-compulsive disorder
Drugs (eg, methylphenidate
Movements are idiosyncratic, nonrhythmic, rapid, suppressible, and repetitive; they occur almost unconsciously.
Tics can be suppressed only for brief periods and with conscious effort.
Tics may be simple or complex. Simple tics (eg, eye blinking) often begin as nervous mannerisms in childhood or later, then disappear spontaneously.
Tics tend to be more complex than myoclonus and less flowing than chorea.
Parkinson’s disease, disorders and drugs that cause parkinsonism (see Table 4: Movement and Cerebellar Disorders: Some Causes of Parkinsonism)
Movements are regular and alternating or oscillatory.
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