Parkinson disease is a disorder that gradually destroys cells in certain regions of the brain involved in moving the body. Symptoms include trembling hands, rigid muscles, slow movement, and problems with balance. The disease is named for English physician James Parkinson, who first described the condition in his 1817 work An Essay on the Shaking Palsy. The condition is often called Parkinson’s disease. However, many medical organizations prefer the term Parkinson disease, to emphasize the patient rather than the person who first described the condition.
Symptoms
of Parkinson disease occur because the condition gradually kills nerve cells that release dopamine. Dopamine is a neurotransmitter, a chemical that carries messages from one nerve cell to another. Loss of dopamine disrupts communication pathways among nerves that help control movement.
As more cells die, patients have increasing difficulty controlling certain movements. A person with Parkinson disease often walks with a shuffle and finds it hard to write clearly or button clothes. Face muscles may grow rigid, causing a “masklike” expression. Patients may have trouble beginning such movements as rising from a chair. The disease may have psychological effects, including depression and dementia (decreased mental ability). The condition may cause serious disability.
Causes.
Doctors do not know what causes the most common form of Parkinson disease, which occurs chiefly in people 50 to 70 years old. Some rare forms of the disease that tend to strike people less than 50 years old are caused by defects in genes (chemical units of heredity). But research suggests that most cases are not caused by genetic abnormalities.
Parkinson disease due to unknown causes is the most common form of a group of disorders with similar symptoms called Parkinsonism. Other causes of Parkinsonism include certain drugs and exposure to toxic quantities of carbon monoxide.
Treatment with drugs.
One of most effective approaches to treatment aims to replace the brain’s lost dopamine. Dopamine itself cannot be given as a drug, because it does not cross from the bloodstream into the brain. But a drug called levodopa or L-dopa does enter the brain, where surviving nerve cells transform it into dopamine. For many patients, L-dopa at first brings dramatic improvement in symptoms. But as the disease progresses, L-dopa becomes less effective in most patients. Many patients also develop troubling side effects, including abnormal movement, sudden changes in muscle control, sleeplessness, vivid nightmares, hallucinations, and confusion. See Dopamine .
Drugs called dopamine receptor agonists behave somewhat like dopamine in the brain. Dopamine receptor agonists include pergolide, bromocriptine, pramipexole, and ropinirole. Many patients take these drugs in combination with L-dopa.
Drugs called anticholinergics also help control some symptoms, particularly trembling. Still other drugs increase the amount of dopamine available by inhibiting the action of substances that break down L-dopa. Two of these drugs are tolcapone and entacapone.
Another drug that relieves symptoms, called selegiline, has raised interest as a possible means to prevent some of the nerve damage that occurs in Parkinson disease. But studies have failed to produce strong evidence that selegiline slows progression of the disease.
Other treatments.
In some cases, doctors may use surgery to destroy particular areas of the brain that produce symptoms of Parkinson disease. Two of these surgical procedures are called thalamotomy and pallidotomy. Another approach involves implanting a device called a deep brain stimulation system that delivers electrical pulses to certain areas of the brain. Researchers continue to explore the possibility of replacing Parkinson patients’ lost dopamine-producing cells with transplanted cells from other sources.
See also Dementia
