What is the Connection Between Parkinson's and Dementia?

Parkinson's is a disease which affects the brain, causing problems with movement. The muscles become stiff and sometimes shake, and the person moves more slowly than normal. Parkinson's and dementia are linked because, in some people with Parkinson's disease, dementia may occur as the illness progresses. Dementia is a disorder in which brain function deteriorates, leading to difficulties with remembering, planning and organizing, recognizing people and things, and communicating with others.

Early Parkinson's symptoms tend to develop gradually, and one of the first signs of Parkinson's disease may be unusually tense muscles, which may prevent the arms from swinging normally while walking. As movement slows, a shuffling style of walking may arise, and the upper limbs, hands or fingers might begin to shake in what are referred to as Parkinson's tremors. Although an individual's Parkinson's prognosis can vary in terms of how quickly the disease progresses, the illness tends to worsen over time. In early onset Parkinson's, where people develop the condition before the age of 50, dementia rarely occurs, but, in those who develop the disease later, up to 40 percent have both Parkinson's and dementia.

There are a number of causes of dementia, with Alzheimer's being the most common example. The symptoms of dementia vary depending on the cause, and in the case of Parkinson's and dementia, there are difficulties in the areas of reasoning, planning, making decisions and adapting to changes in routine. Forgetfulness is also a symptom, and slow thinking, although slowness of thought is also found in Parkinson's patients who do not have dementia. In extreme cases, people may hallucinate and hold strange beliefs, and sometimes they may become distressed or angry. Symptoms can vary over the course of a day, and some may also be found in people who have Parkinson's and depression, making diagnosis difficult.

Where Parkinson's and dementia are found together, what are known as comorbid conditions of dementia, other illnesses such as depression occurring at the same time, can have overlapping symptoms. It can be a complex problem trying to work out whether the true cause of dementia symptoms might actually be depression, medication the person is taking, or another condition such as an infection or head injury, or whether these factors are all simply existing alongside the dementia. Sometimes the Parkinson's drugs themselves may be causing symptoms, and a particular drug may need to be reduced or stopped. This has to be balanced against the need for the patient to remain mobile.

Treatment of Parkinson's and dementia generally involves assessing how much of a problem dementia symptoms are for the person. Hallucinations may worry carers yet not be distressing for the person with Parkinson's, and in some cases it may be more important to maintain mobility and avoid side effects caused by anti-psychotic drugs than to treat symptoms. Usually an expert is required to weigh the potential benefits of treatment against the difficulties associated with leaving the condition as it is. Carers can help by learning how best to communicate with and respond to a person with Parkinson's and dementia.