In 1817, English apothecary James Parkinson documented a “shaking palsy” in some of his patients. Today the disease that bears his name remains a sobering medical reality: approximately one million Americans suffer from Parkinson’s disease (PD) and about 50,000 new cases are diagnosed each year.
As it is a neurodegenerative disease, PD is a progressive condition. It results from deterioration in an area of the brain known as the substantia nigra, a region of cells that control movement. The primary job of these cells is to produce a substance known as dopamine—one of many substances called “neurotransmitters” that facilitate communication between brain cells (neurons).
No scan or lab test is available by which to diagnose PD, leaving the condition only identifiable by way of its symptoms and physical manifestations. The disease begins insidiously and progresses gradually, often emerging as a barely detectable hand tremor. This might be followed by loss of facial expression, difficulty initiating movement, mumbled speech, or a lack of arm-swinging while walking. In advanced stages of PD, dementia may manifest.
Additional problems known to affect people with PD include sleep disturbances, difficulty swallowing and chewing, problems with urination, constipation, and loss of libido. It should be noted that several other diseases are comprised of some of these symptoms and can easily be confused with PD. For example, multiple symptoms of Alzheimer’s disease overlap those of PD.
Though the precise cause of PD remains unknown, research has raised the likelihood that a variety of factors may be involved. Changes in a person’s genes, either by way of inherited or environmental factors, are suspected. Toxins or certain viruses in a person’s environment may also trigger signs of the disease.
Certain risk factors for developing Parkinson’s disease have also been identified. People with family members who manifest the disease have increased risk for PD, although not to a great extent. Research indicates men are more likely to develop the condition than are women, and the disease seldom occurs in anyone before late middle-age. Constant exposure to certain herbicides and pesticides has been associated with a greater risk of Parkinson’s disease.
Changes in brain chemistry are characteristic of Parkinson’s disease patients. One noteworthy neurological alteration is the loss or failure of a special collection of cells in the brain that produce dopamine, a chemical messenger. Many of the neurons that communicate by way of dopamine are involved in movement. Norepinephrine—a neurotransmitter involved with the autonomic part of the nervous system—is also deficient in the brains of PD patients, a fact that can influence digestion and blood pressure regulation.
Despite the unanswered questions and harsh symptoms that remain aligned with Parkinson’s disease, medications for the condition can yield a dramatic and positive effect. The most effective of these medications, levodopa, is a natural substance that (when taken as a pill) converts to dopamine inside the brain. However, this drug has to be combined with a drug called carbidopa that prevents levodopa’s conversion to dopamine before it reaches the brain. The combination of these drugs— known as Sinemet—helps a patient avoid potential side effects, particularly nausea.
After prolonged use of the drug, however, the effects of Sinemet tend to wear off at an accelerated rate. Further complicating matters, the Sinemet dosage sometimes has to be lowered to reduce side effects. Both of these issues lead to poorer control of the symptoms of PD.
Drugs that mimic the effects of dopamine, called dopamine agonists, are also used in the treatment of Parkinson’s disease, but they tend to be less effective than those drugs previously mentioned. On the other hand, dopamine agonists do not tend to wear off as quickly and can be used to help smooth out the waxing and waning of Sinemet.
Medications used in the treatment of PD have many unpleasant side-effects. These include hallucinations, involuntary jerking of the extremities, drowsiness, nausea, and a sudden drop in blood pressure upon standing. In addition to use of medications, surgery can play a role in treatment of PD symptoms. Typically, however, such measures are reserved for patients who suffer disabling side effects from medications or who experience poor control of their symptoms.
Until recently, surgical treatment of PD had involved placement of a small probe into a particular area of the brain, destroying that area and resulting in diminished tremor and improved movement. Lately, however, use of a small electrode in a different area of the brain has proven more effective. During surgery, this electrode is connected to a continuous stimulator that is permanently implanted under the patient’s skin. Like any surgery, this procedure (called Deep Brain Stimulation) has risks, such as infection or brain injury caused by bleeding or stroke. Such outcomes, however, are rare.