Risk Factors for Parkinson's Disease

Parkinson's disease affects people worldwide, including more than a million people in North America.

Age and Gender. The average age of onset is 55. The elderly are at higher risk for both parkinsonism and Parkinson's disease, although there is some evidence that the very elderly (over 75) are at low or no risk. About 10% of Parkinson's cases are in people younger than 40 years old. Having a first-degree relative who develops Parkinson's after age 50 does not usually pose any higher than average risk; having a parent or sibling with the disease earlier than age 50, however, does. One study suggested that the disease progresses more rapidly in men than women, but these results may have only indicate that men are less responsive to the treatments for Parkinson's. Older women seem to be more at risk for gait disturbance and men for rigidity and tremor.

Relatives. People with siblings or parents who developed Parkinson's at a younger age are at higher risk for Parkinson's disease, but relatives of those who were elderly when they had the disease appear to have an average risk.

Ethnicity and Geography. African- and Asian-Americans have a lower risk than European-Americans. A higher incidence of parkinsonism is found in people who live in rural areas, particularly those who drink private well water or are agricultural workers exposed to pesticides and herbicides. These risks, however, seem to vary depending on ethnicity, indicating that genetic factors are also at work.

Smoking. Cigarette smokers appear to have a lower risk for Parkinson's disease, This finding, of course, is no excuse to smoke, but such protection may help researchers develop new therapies.

Risk Factors for Parkinsonism

The symptoms of parkinsonism (tremor, gait disturbance, bradykinesia, and rigidity) appear in an estimated 8 million people over 65. In one study, parkinsonism occurred in about 15% of people 65 to 74 years of age, about 30% in those 75 to 84, and over half of people older than 85. It should be noted that this particular study included people with very mild symptoms and the percentages are higher than ones using stricter criteria.

How Serious Is Parkinson's Disease?

General Outlook

Parkinson's disease is not fatal, but it reduces longevity. It also seriously impairs the quality of life and may sometimes lead to severe incapacity within 10 to 20 years. Treatments are increasingly effective however in alleviating symptoms and even slowing progression of the disease. Over time, however, the side effects of many of these medications can be nearly as distressing as the disease itself, and the drugs may eventually lose their effectiveness. Parkinson's disease is sometimes categorized as either tremor predominant or postural instability and gait disturbed (PIGD). In younger patients tremor is usually predominant and progression of the disease is slow. Elderly people are more apt to have PIGD. Some studies have suggested that early PIGD symptoms predict a faster decline than having tremor predominant. Gait disturbance is a particularly serious sign in the elderly.

Impact on Emotions and Mental Status

The emotional and psychiatric impacts of the symptoms are devastating. Depression is extremely common, although one study found that only about 7% of patients met the criteria for major depression. Such patients were generally much older and already had mental or psychiatric problems. Depression in the remaining population was generally mild and most likely due to the emotional effect of the disease on the lives of both patients and their families -- not actual physical changes in the brain. Dementia is about six times more common in the elderly Parkinson patient than in the average older adult. In one study, 28% of all patients and two thirds of those over 85 had dementia. Nearly all drug treatments used for Parkinson's disease have side effects that cause neurologic and psychiatric disturbances. The physical and emotional impact on the family should not be underestimated as the patient becomes increasingly dependent on their support.

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