Neurological disorder causing progressive loss of control of movement. It was first described in 1817 by British physician James Parkinson (1755–1824). The cause of primary parkinsonism, or Parkinson disease, is unknown. The mean age of onset is about 57, but juvenile parkinsonism is also known. Neurons in the brain that normally produce dopamine deteriorate. When 60–80percnt are destroyed, signals suppressing unintended movement are disrupted and symptoms appear, including tremor at rest, muscle rigidity, trouble in starting movements, and loss of balance. Known causes include sleeping sickness; certain poisons; repeated blows to the head, as in boxing; and the drug MPTP. Environmental toxins or genetic susceptibility may account for some cases. Drug therapy requires careful scheduling and combinations to delay development of tolerance and side effects. Surgical pallidotomy (destruction of the globus pallidus, a brain structure involved in motor control) and transplantation of fetal dopamine-producing tissue remain experimental.
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Loss or impairment of voluntary use of one or more muscles. It may be flaccid (with loss of muscle tone) or spastic (stiff). Hemiplegia (one-sided paralysis) is usually caused by stroke or brain tumour on the opposite side. Diplegia (two-sided paralysis, as in cerebral palsy) results from generalized brain disease. Spinal-cord damage (from bone or joint disease, fracture, or tumour affecting the vertebrae; inflammatory and degenerative diseases; or pernicious anemia) paralyzes the body at and below the level of the damage (paraplegia if the legs and lower body only; quadriplegia if arms and legs). Poliomyelitis and polyneuritis (neuritis of multiple nerves) result in paralysis with muscle wasting. Bell palsy (a type of neuritis) paralyzes the muscles of one side of the face. Muscular dystrophy causes paralysis by attacking muscle. Metabolic causes include myasthenia gravis. Paralysis may also have psychiatric causes (see hysteria).
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Paralysis resulting from abnormal development or damage to the brain before or soon after birth. Cases are of four main types: spastic, with spasms contracting the extremities and often also with intellectual disability and epilepsy; athetoid, with slow, changing spasms in the face, neck, and extremities, grimacing, and inarticulate speech (dysarthria); ataxic, with poor coordination, muscle weakness, an unsteady gait, and difficulty performing rapid or fine movements; and mixed, in which symptoms of two or more types are present.
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