In Parkinson’s disease, cells in the substantia nigra, a brain region that produces
substantial amounts of dopamine, gradually die off. The loss of this neurotransmitter disrupts circuits within the brain’s movement systems, leading to the disease’s characteristic shuffling gait and tremor.
Parkinson’s disease occurs when cells located in a small area of the brain known as the substantia nigra become damaged or destroyed and stop producing dopamine. This causes slowed movements, rigidity, and tremors.
James Parkinson wrote a seminal text on "the shaking palsy" in 1817. The English apothecary outlined the condition’s symptoms so definitively — trembling, stiffness, trouble speaking and walking, balance and coordination problems, even memory issues and depression — that the disease has become forever linked to his name.
—Each year, approximately 50,000 to 60,000 Americans are diagnosed with Parkinson’s, joining more than a million people already living with the disease in the United States.
—The average age of diagnosis is 60, and risk increases further with age, although 5 to 10 percent of patients have an "early onset" form that develops before they turn 50.
—Men are 50 percent more likely to get Parkinson’s.
—The annual cost of treatment, disability payments, and lost income from Parkinson’s is almost $25 billion in the United States alone.
Parkinson’s disease is not fatal, but it gets worse over time and has no cure. With support from the National Institutes of Health and other funding agencies around the globe, however, researchers have developed treatments that help people remain active and functional for many years after their diagnosis.
Perhaps the biggest breakthrough came in the 1960s, when scientists discovered levodopa, or L-dopa, a naturally occurring chemical that turns into dopamine in the brain. Giving Parkinson’s patients L-dopa alleviates many of their motor problems, including rigidity and slowed movement, and approximately 70 to 80 percent now take the medication.
Unfortunately, L-dopa can have serious side effects, including involuntary movements and hallucinations, and the drug tends to work for shorter periods over time. Thus, in recent years, scientists have developed drugs that extend L-dopa’s longevity while minimizing side effects. Carbidopa and other drugs, for instance, block enzymes that break down L-dopa before it can reach the brain.
Other medications are called dopamine agonists, because although chemically different, they act like dopamine. When used on newly diagnosed patients, these drugs extend the overall time that drug therapy is effective.
Until the discovery of L-dopa, surgery was a common treatment for Parkinson’s; by destroying certain brain regions, doctors could reduce some symptoms. In the past decade, surgical treatment has regained favor as scientists gain new insights from animal models and other research.
Increasingly, physicians use deep brain stimulation, in which electrodes are inserted into the brain, usually into regions known as the globus pallidus and subthalamic nucleus. In many cases, symptoms noticeably improve after doctors calibrate the timing and intensity of the electrical pulses. Surgical lesions that disable these areas of the brain are still used on occasion.