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

Parkinson's and dementia are separate conditions, with many people developing one without the other. This said, people with Parkinson's have a higher risk of dementia, particularly during old age. The two main types of dementia that people with Parkinson's can develop are 'Parkinson's dementia' and 'dementia with Lewy bodies'.

Parkinson's disease and dementia

Parkinson's disease and dementia are both progressive conditions that get worse over time. They are also both far more common among the older population:

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.

Parkinson's disease

What: The brain cells and nerve cells responsible for coordinating how your muscles move become affected by changes in the structure of your nervous system. This means that your ability to move in a smooth and efficient way gradually declines.

Symptoms: The main symptoms are shaking (tremors), stiffness, and slowness of movement. There are also many other possible symptoms that may develop as the disease progresses that affect both your physical and mental wellbeing.

Dementia

What: The cells and nerves in the part of the brain responsible for your cognitive functioning are damaged or lost. This causes significant mental deterioration which affects everyday life.

Symptoms: The decline in this area of your brain typically leads to difficulties with memory, thinking, reasoning, recalling appropriate language and social behaviour.

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."

Parkinson's and dementia common misconceptions

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

Does Parkinson's disease always lead to dementia?

No. While Parkinson's disease means you have an increased risk of developing dementia, roughly half of people with Parkinson's won't develop dementia symptoms.

Does Parkinson's cause dementia?

Experts believe that Parkinson's alone does not directly cause dementia, although it does increase the risk along with other age-related factors. If dementia does occur, it typically develops in people with Parkinson's who are over 70 years.

Is Parkinson's a form of dementia?

Parkinson's disease is not a form of dementia and it often develops completely independently of dementia. However, you may have heard the term "Parkinson's dementia" - this refers to a form of dementia that only affects people with Parkinson's. The important distinction is that not everyone with Parkinson's develops this.

How is Parkinson's related to dementia?

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:

Physical symptoms could include:

Mental symptoms could include:

  • Memory loss.
  • Thinking more slowly.
  • Difficulty with understanding, planning or making judgements.
  • Language problems.
  • Visual hallucinations or delusions.
  • Fluctuating consciousness.
  • Sleep problems.

"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.

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