Voluntary movement requires complex interaction of the corticospinal (pyramidal) tracts, basal ganglia, and cerebellum (the center for motor coordination) to ensure smooth, purposeful movement without extraneous muscular contractions. 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 sometimes called extrapyramidal disorders.

Classification

Movement disorders are commonly classified as those with decreased or slow movement (hypokinetic disorders) and those with increased movement (hyperkinetic disorders). The classic and most common hypokinetic disorder is Parkinson disease. Hyperkinetic disorders include tremor, myoclonus, dystonia, chorea (including hemiballismus [rapid chorea] and athetosis [slow chorea]), and tics. However, this classification does not account for overlap between categories (eg, tremors that occur in Parkinson disease).

Hyperkinetic disorders

Hyperkinetic disorders can be rhythmic or nonrhythmic (see Movement and Cerebellar Disorders: Classification of common hyperkinetic disorders. and see Movement and Cerebellar Disorders: Hyperkinetic Disorders).

Rhythmic disorders are primarily tremors—regular alternating or oscillatory movements, which can occur mainly at rest, while maintaining a position, or during attempted movement. However, in some cases, a tremor, though rhythmic, is irregular, as occurs when tremor is associated with dystonic disorders.

Nonrhythmic hyperkinetic disorders can be slow (eg, athetosis), sustained (eg, dystonias), or rapid (eg, myoclonus, chorea, tics, hemiballismus). Rapid hyperkinetic disorders may be suppressible (eg, tics) or nonsuppressible (eg, hemiballismus, chorea, myoclonus). Athetosis and chorea may occur together as choreoathetosis. Chorea is the most characteristic movement disorder in Huntington disease (see Movement and Cerebellar Disorders: Huntington Disease). Multiple motor and phonatory tics are the defining feature of Tourette syndrome (see Neurologic Disorders in Children: Tourette's Syndrome).

Fig. 1
Classification of common hyperkinetic disorders.

Table 1
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Hyperkinetic Disorders Abnormal Movement Causes Description Athetosis Huntington disease, encephalitis, hepatic encephalopathy Drugs (eg, cocaine, amphetamines, antipsychotics) Movements are nonrhythmic, slow, writhing, and sinuous, primarily in distal muscles; alternating postures of the proximal limbs often blend continuously to produce a flowing stream of movement. Athetosis has features of dystonia and chorea and often occurs with chorea as choreoathetosis. Chorea Huntington disease, hyperthyroidism, hypoparathyroidism, paraneoplastic syndromes, SLE affecting the CNS, other autoimmune disorders, rheumatic fever, tumors or infarcts of the caudate nucleus or putamen Pregnancy, often in women who had rheumatic fever Senile chorea Drugs that can cause chorea (eg, levodopa, phenytoin, cocaine, oral contraceptives) Drugs that can cause tardive dyskinesia (eg, antipsychotics) Movements are nonrhythmic, jerky, rapid, and nonsuppressible, primarily in distal muscles or the face. Sometimes abnormal movements are incorporated into semipurposeful acts that mask the involuntary movements. Chorea often occurs with athetosis as choreoathetosis. Dystonias Primary (idiopathic) Degenerative or metabolic disorders (eg, Wilson disease, PKAN due to a PANK2 mutation [previously, Hallervorden-Spatz disease], various lipidoses, multiple sclerosis, cerebral palsy, stroke, brain hypoxia) Drugs that block dopamine receptors, most often antipsychotics (eg, phenothiazines, thioxanthenes, butyrophenones) or antiemetics Sustained muscle contractions often distort body posture or cause twisting, repetitive movements. Hemiballismus Lesions (most often due to stroke) in the contralateral subthalamic nucleus or in connecting afferent or efferent pathways Movements are nonrhythmic, rapid, nonsuppressible, violent, and flinging. Myoclonus See Table 2: Movement and Cerebellar Disorders: Causes of Myoclonus. Very rapid and jerky, nonsuppressible, shocklike twitches occur; they may be focal, segmental, or generalized. Tics Primary: Tourette syndrome Secondary: Huntington disease, neuroacanthocytosis, PKAN, infections, stroke, drugs (eg, methylphenidate, cocaine, amphetamines) Movements are nonrhythmic, stereotypical, rapid, and repetitive; characteristically, patients have an urge to do them and feel brief relief after doing them. Tics can be suppressed only for brief periods and with conscious effort. Tics may be motor or phonatory; they may be simple (eg, eye blinking, growling, clearing the throat) or complex (eg, shoulder shrugging, arm swinging, shouting words or sentences, including obscenities). Tremor Essential tremor Parkinson disease, Wilson disease Certain drugs (eg, lithium, valproate, olanzapine, other typical and atypical antipsychotics—see Movement and Cerebellar Disorders: Some Causes of Secondary and Atypical Parkinsonism) Movements are regular, mostly rhythmic, and oscillatory. PKAN = pantothenate kinase‒associated neurodegeneration.

Last full review/revision January 2013 by Hector A. Gonzalez-Usigli, MD; Alberto Espay