A Parkinson's Disease Primer

Article excerpt

An ongoing CE program of The University of Florida College of Pharmacy and DRUG TOPICS

An "involuntary tremulous motion, which lessened muscular power, in parts not in action and even when supported: with a propensity to bend the trunk forward, and to pass from a walking to a running pace, the senses and intellects being uninjured" is how Dr. James Parkinson first described Parkinson' s disease (PD) in a case series describing six individuals with "shaky palsy." Since then, Parkinsons disease affects an estimated one million people in the United States and millions worldwide. Parkinson s disease ultimately results from loss of dopamine-producing brain cells over time which leads to both movement and non-movement abnormalities and a decreased quality of life. Despite the therapies available, there is not a cure for PD at this time. Pharmacists are essential in drug therapy management of Parkinson' s disease patients and have an opportunity to provide support to both patients and their caregivers.

Epidemiology

Parkinson' s disease is the second most common neurodegenerative disorder following Alzheimer's disease. It is estimated that four to six million people around the world suffer from the condition, with 60,000 new cases diagnosed each year in the United States, adding to the already 1.5 million Americans who currently have PD.

Parkinson's disease affects men and women in almost equal numbers. The average age of onset of the disease is 60 years of age, affecting one in 100 people over the age of 60. With the elderly population expected to increase, the incidence and prevalence of PD will increase as well. According to the National Institute of Neurological Disorders and Stroke, Parkinson s disease costs the nation an excess of approximately $6 billion annually, including treatment, social security payments, and lost income from inability to work.

Etiology

Although much research has been conducted to discover the possible causes of Parkinson's disease, an exact etiology has still not been determined. Etiologies that have been investigated for PD include genetic inheritance and environmental exposure to toxins, or a combination of both.

Genetic factors are often viewed as a starting point in trying to unravel the cause of any disease state-particularly one of neurologic origin. About 15%-25% of people with Parkinsons report having a relative with the disease. In fact, large epidemiologic studies have found that people having an affected first-degree relative have a two- to threefold increased risk of developing Parkinsons. Research has postulated that genetics may play a larger role in younger onset PD cases. However, with all the completed genetic research to date, a specific gene or set of genes causing PD has not been identified.

Alternatively, some researchers theorize that Parkinsons disease may result from exposure to an environmental toxin or injury. Such exposures to rural living, well-water consumption, and pesticides or herbicides have all been linked to increased risk of Parkinsons disease. However, there is no conclusive evidence that any one environmental factor can be considered the sole cause of the disease. Most experts agree that Parkinsons is caused by a combination of genetic and environmental factors.

Parkinson's disease may result from other causes such as brain tumors near the basal ganglia, atherosclerosis of the cerebral blood vessels, or head trauma. Most commonly, however, drugs such as antipsychotics, some antiemetics, and other agents cause clinical manifestations of the disease. (See Table 1.)

Pathophysiology overview

Regardless of the exact etiology, much is known about the resulting primary pathology of Parkinsons disease. Dopamine is an inhibitory neurotransminer of acetylcholine, an excitatory neurotransmitter. Dopamine is synthesized and stored in the substantia nigra, then transported to the striatum. Under normal conditions and through a complex sequence of stimulatory and inhibitory neuronal pathways, striaral neurons communicate with neurons of the thalamocortical pathway. …