What is the link between Parkinson's disease and dementia?

Parkinson's disease and dementia

Doença de Parkinson e demência are both progressive conditions that get worse over time. They are also both far more common among the older population:

• 96% of Parkinson's disease cases occur in those over 50.

• 95% of dementia cases in those over 65.

What's more, a person with Parkinson's disease (commonly shortened to Parkinson's) may have a higher chance of developing dementia at some stage. It's thought that this happens in roughly half of all people with Parkinson's. Results of studies that tracked patients over 10 years and eight years respectively suggest that dementia is diagnosed in between 30% and almost 80% of people with Parkinson's.

Yet, it's important to understand Parkinson's and dementia as two different degenerative conditions:

• They don't have the same primary causes or primary symptoms.

• It's common to develop one without the other.

When Parkinson's and dementia symptoms are similar

Parkinson's and dementia can also lead to similar symptoms. Although Parkinson's is often thought of as a disease that only interferes with movement, it can also lead to thinking and memory issues. Dr Katherine Fletcher, research communications manager at Parkinson's UK, explains:

"Parkinson's can impact memory, thinking and concentration, with some people experiencing this more mildly than others. However, if thinking and memory problems are serious enough to affect someone's ability to carry out everyday tasks then they may be diagnosed with dementia."

The link between Parkinson's and dementia can be confusing. Here are some common questions:

While Parkinson's and dementia are completely independent conditions, people with Parkinson's have a higher chance of developing certain forms of dementia.

"There are two main types of dementia that affect some people with Parkinson's: Parkinson's dementia and dementia with Lewy bodies," says Fletcher.

Parkinson's dementia and dementia with Lewy bodies

"Both of these types of dementia involve abnormal protein deposits called Lewy bodies forming in brain cells. Because they are so similar, you may hear both of them being called Lewy body dementia."

According to Fletcher, the symptoms of Parkinson's dementia and dementia with Lewy bodies can be very similar. These include both motor (physical) and cognitive (mental) symptoms:

"However, the order in which movement and mental symptoms appear is different," adds Fletcher. "If there have been motor symptoms (such as tremor or rigidity) for at least one year before dementia symptoms occur, specialists will often give a diagnosis of Parkinson's dementia.

"If dementia symptoms occur before or at the same time as motor symptoms, specialists will usually give a diagnosis of dementia with Lewy bodies."

Seeking a diagnosis

If you already have a diagnosis of Parkinson's, you may mistake your symptoms as a sign of this condition and a diagnosis of Lewy body dementia can go undetected. If your symptoms appear to have escalated more quickly than usual over the course of a few months, it may be a sign that you have developed dementia.

Although it can feel difficult and even embarrassing to reach out for help if you notice symptoms worsening and disrupting day-to-day tasks, getting diagnosed means you can be offered better treatment and support. There is no single test for Lewy body dementia but your GP may carry out a number of assessments including urine and blood tests and brain scans.

You can also contact the Parkinson's UK helpline on 0808 800 0303 for more information on both Parkinson's and dementia.