Dyskinesias are movement disorders that can be caused by neurological conditions or psychiatric drugs. They include dystonias, hypokinesias, choreas, and tics, and can result in involuntary muscle spasms or decreased ability to perform voluntary movements. Parkinson’s disease and tardive dyskinesias are examples of dyskinesias.
A dyskinesia is one of many similar disorders of voluntary muscle movement. Sometimes these are characterized by a decreased ability to perform voluntary movements such as walking or standing up, but they also occur as involuntary muscle spasms causing sudden tics. Many are symptoms of neurological disorders such as Parkinson’s or Huntington’s disease. A small number of psychiatric drugs that affect neurotransmitter function in the brain can cause dyskinesias as side effects in individuals who have certain mental illnesses and genetic risk factors.
Movement disorders that impair or reduce voluntary movement or cause involuntary muscle contractions are called dyskinesias. They are often caused by neurological conditions, including neurodegenerative diseases, particularly those affecting the basal ganglia and cerebellum of the brain. Some dyskinesias, called dystonias, cause unusual movements even in patients who are still or at rest. Dystonias cause muscle contractions powerful enough to twist the limbs into abnormal, twisted postures. Hypokinesias are a subclass of disorders that involve an inability to move, called akinesia, and slow movements, called bradykinesia.
Choreas are dyskinesias with random, abrupt movements that can be brief or become bursts of long, violent activity. They result from disorders including metal poisoning, Huntington’s disease, and various disorders of the basal ganglia and cerebellum of the brain. Named after the Greek word for dance, a chorea can manifest as an inability to maintain a desired posture, dropping objects, and especially random, dance-like movements. Some of these are characterized by slow, writhing movements, while other forms, called balismas, can be intense to the point where patients squirm or jump.
Parkinson’s disease is accompanied by various dyskinesias, including difficulty walking, which occur as the neurological damage of the condition progresses. This happens in part due to cell death in brain regions such as the substantia nigra, one of the pathways that control movement coordination and execution. In many patients, disruption of cerebellar guidance pathways in the brain causes shuffling and impaired gait along with loss of balance. Furthermore, many parkinsonian patients treated with the drug levadopa develop secondary progressive dyskinesia after several years of treatment with this drug. Hemiballismus, a condition with similarities to Parkinson’s, is rarer and has a unique pathology in which patients experience involuntary and violent throwing of the limbs.
Tardive dyskinesias are involuntary movements of muscle groups and occur in some patients as a side effect of treatment with psychiatric drugs that block the effects of dopamine, an important chemical messenger for regulating movement stability in the brain. The incidence of tardive dyskinesia varies greatly among patients and is highest among schizophrenics. Another class of movement disorders are tics, sudden and repetitive movements of muscle groups, which are sometimes accompanied by loss of vocal and not just muscle control. Severe motor tics can arise in conditions such as Tourette’s syndrome and genetic disorders such as Huntington’s disease.
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