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Parkinson Disease !p@r-kun-sunz-di-!zEz

(Parkinson's Disease)

by Hector A. Gonzalez-Usigli, MD, Alberto Espay, MD

Parkinson disease is a slowly progressive degenerative disorder of the central nervous system (brain and spinal cord). It is characterized by tremor when muscles are at rest (resting tremor), increased muscle tone (stiffness, or rigidity), slowness of voluntary movements, and difficulty maintaining balance (postural instability). In many people, thinking becomes impaired, or dementia develops.

  • Parkinson disease results from degeneration in the part of the brain that helps coordinate movements.

  • Often, the most obvious symptom is tremors that occur when muscles are relaxed.

  • Muscles become stiff, movements become slow and uncoordinated, and balance is easily lost.

  • Doctors base the diagnosis on symptoms.

  • Changes in lifestyle, drugs (such as levodopa plus carbidopa), and sometimes surgery help lessen symptoms, but the disease is progressive, eventually causing severe disability and immobility.

Parkinson disease is the second most common degenerative disorder of the central nervous system after Alzheimer disease. It affects about 1 of 250 people older than 40, about 1 of 100 people older than 65, and about 1 of 10 people older than 80. It commonly begins between the ages of 50 and 79. Rarely, Parkinson disease occurs in children or adolescents.

When the brain initiates an impulse to move a muscle (for example, to lift an arm), the impulse passes through the basal ganglia (collections of nerve cells located deep within the brain). The basal ganglia help smooth out muscle movements and coordinate changes in posture. Like all nerve cells, those in the basal ganglia release chemical messengers (neurotransmitters) that trigger the next nerve cell in the pathway to send an impulse. A key neurotransmitter in the basal ganglia is dopamine . Its overall effect is to increase nerve impulses to muscles. In Parkinson disease, nerve cells in part of the basal ganglia (called the substantia nigra) degenerate, reducing the production of dopamine and the number of connections between nerve cells in the basal ganglia. As a result, the basal ganglia cannot smooth out movements as they normally do, leading to tremor, loss of coordination, slow movement (bradykinesia), a tendency to move less (hypokinesia), and problems with posture and walking.

What causes Parkinson disease is unclear. According to one theory, Parkinson disease may result from abnormal deposits of synuclein (a protein in the brain that helps nerve cells communicate). These deposits, called Lewy bodies, can accumulate in several regions of the brain, particularly in the substantia nigra (deep within the cerebrum) and interfere with brain function. Lewy bodies often accumulate in other parts of the brain and nervous system, suggesting that they may be involved in other disorders. In Lewy body dementia, Lewy bodies form throughout the outer layer of the brain (cerebral cortex). Lewy bodies may also be involved in Alzheimer disease, possibly explaining why about one third of people with Parkinson disease have symptoms of Alzheimer disease.

About 15 to 20% of people with Parkinson disease have relatives who have or have had the disease. Thus, genetics may play a role.

Parkinsonism causes the same symptoms as Parkinson disease but is caused by various other conditions, such as multiple system atrophy, progressive supranuclear palsy, stroke, head injury, or certain drugs (see Parkinsonism).

Did You Know...

  • Many other disorders and drugs can cause symptoms similar to those of Parkinson disease.

  • Parkinson disease is sometimes hard to diagnose in older people because aging causes some of the same symptoms.

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