Parkinson’s disease (PD) is an age-related degenerative disorder of certain brain cells. It mainly affects movements of the body, but other problems, including dementia, may occur. It is not considered a hereditary disease, although a genetic link has been identified in a small number of families.

• The most common symptoms of Parkinson’s disease are tremor (shaking or trembling) of the hands, arms, jaw, and face; rigidity (stiffness) of the trunk and limbs; slowness of movement; and loss of balance and coordination.
• Other symptoms include shuffling, speaking difficulties, (or speaking very softly), facial masking (expressionless, mask-like face), swallowing problems, and stooped posture.
• The symptoms worsen gradually over years.
Depression, anxiety, personality and behavior changes, sleep disturbances, and sexual problems are commonly associated with Parkinson’s disease. In many cases, Parkinson’s disease does not affect a person’s ability to think, reason, learn, or remember (cognitive processes).
• In some people with Parkinson’s disease, however, one or more cognitive processes are impaired.
• If this impairment is severe enough to interfere with the person’s ability to carry out everyday activities, it is called dementia. Fortunately, dementia occurs in only about 20% of people with Parkinson’s disease. If Parkinson’s disease patients experience hallucinations and have severe motor control, they are at higher risk for dementia. The development of dementia is slow. Typically, people that develop symptoms of dementia do so about 10 to 15 years after the initial diagnosis of Parkinson’s disease.

Parkinson's Disease Dementia OverviewAbout 500,000 people in the United States have Parkinson’s disease, and about 50,000 new cases are diagnosed each year. The number of those who have some cognitive symptoms is difficult to pinpoint because accurate data are lacking for the following reasons:

• Researchers use various definitions of cognitive impairment and dementia.
• Parkinson’s disease often overlaps with other degenerative brain disorders that can cause dementia, such as Alzheimer’s disease and vascular disease within the brain.
• Some researchers suggest that at least 50% of people with Parkinson’s disease have some mild cognitive impairment and estimate that as many as 20% to 40% may have more severe symptoms or dementia.

Most people have the first symptoms of Parkinson’s disease after the age of 60 years, but Parkinson’s disease also affects younger people. Early-onset Parkinson’s disease strikes people around the age of 40 years, or even earlier.

• Regardless of age at onset of the disease, dementia symptoms tend to appear later (after about 10 to 15 years) in the course of the disease.
• Dementia is relatively rare in people with onset of Parkinson’s disease before age 50 years, even when the disease is of long duration.
• Dementia is more common in people with an older age (about 70 years) at onset of Parkinson’s disease.