Parkinson's disease, also known as paralysis agitans, is a relatively common neurodegenerative disorder that usually begins to affect patients between the ages of 45 and 65. According to "Harrison's Principles of Internal Medicine," it afflicts approximately 1 million individuals in the United States, or about 1 percent of those over the age of 55. Its constellation of symptoms was formally recognized as a single disease entity in 1817 by James Parkinson, but the underlying pathophysiological changes in the brain weren't identified until the 1950s.
Cause
When a human being engages in voluntary movement--for example, reaching for a cup on a shelf--neurotransmitters in the brain essentially compete with one another to make sure the correct muscles are activated, whereas interfering muscles are deactivated. In Parkinson's disease, some neurons in an area of the brain that produce the neurotransmitter dopamine are destroyed by a combination of genetic susceptibility and oxidative stress. Oxidative stress is a phenomenon the human body deals with every day and is a byproduct of normal cell metabolism. It can also be increased by exposure to certain pesticides. Because, in this particular brain pathway, dopamine normally works to inhibit the action of unnecessary muscles, the loss of dopamine leads to the activation of interfering movements.
Symptoms
This loss of inhibition results in a tremor that is typically worse at rest. If the patient performs some purposeful action--such as the reaching for a cup described in Section 1--the pathways in the brain that activate the voluntary muscles become strong enough to overcome the interfering activity and the tremor disappears. The disease also results in a generalized difficulty initiating movements caused by a combination of bradykinesia--literally, slowness of movement--and muscle rigidity. For reasons that are poorly understood, Parkinson's disease also results in a variety of non-motor disturbances. These may include depression, anxiety, sleep disturbances and pain. In fact, according to the February 2010 issue of "Movement Disorders," approximately 40 percent of Parkinson's patients experience significant pain as a result of the disease.
Treatment
As of 2010, a consensus had not been reached regarding the optimum therapy for Parkinson's disease. Current medications can alleviate the symptoms but do not slow the progression of the disease. These include levodopa, which is converted to dopamine by the body and is administered as a replacement for the lost neurotransmitter, given in conjunction with carbidopa, which prevents levodopa from being broken down before entering the brain. "Current Medical Diagnosis and Treatment" states that deep brain electrical stimulation is effective in suppressing tremor and may benefit all the major features of Parkinson's disease. Non-surgical or pharmacological measures may include speech therapy, physical therapy and aids to daily living such as bedside rails or nonslip table mats.
References
- "Current Medical Diagnosis & Treatment 2010, Forty-Ninth Edition"; Stephen J. McPhee, Maxine A. Papadakis, Eds.; 2010
- "Harrison's Principles of Internal Medicine, 17e"; Anthony S. Fauci, Eugene Braunwald, Dennis L. Kasper, Stephen L. Hauser, Dan L. Longo, J. Larry Jameson, and Joseph Loscalzo, Eds.; 2008
- "Movement Disorders"; Pain in Parkinson's Disease; Blair Ford MD; Feb 25, 2010
