Parkinson’s disease dementia can look different from person to person, but may cause hallucinations, confusion, agitation, and memory loss in later stages.

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Parkinson's disease dementia is when a person develops changes in their thinking and behavior after being diagnosed with the movement disorder.

While Parkinson's disease is primarily known as a movement disorder, with hallmark symptoms that include a resting tremor, stiffness, and slowness of movement, there are also non-motor symptoms associated with the disease. One of those non-motor symptoms—dementia—occurs in up to 80% of people with Parkinson's disease.

As with all Parkinson's symptoms, dementia manifests differently from one person to the next, but the overarching indicator is cognitive impairment. Here's what you need to know about Parkinson's disease dementia.

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What are the Parkinson's disease dementia criteria?

Many people with Parkinson's disease experience cognitive changes (like difficulty planning and multitasking), but not all of them develop full-blown dementia. So at what point does Parkinson's disease cause dementia?

On average, Parkinson's disease dementia happens about 10 years after a person first starts having movement problems.

"It happens many, many years after someone has developed Parkinson's," Lynda Nwabuobi, MD, assistant professor of clinical neurology at Weill Cornell Parkinson's Disease and Movement Disorders Institute, tells Health. "It can be around 10 to 15 years."

In fact, if someone shows signs of dementia early on in their Parkinson's diagnosis (say, less than a year), it could be that they were misdiagnosed out of the gate. "They might have dementia with Lewy bodies," Dr. Nwabuobi explains.

Timing is the main factor in Lewy body dementia versus Parkinson's disease dementia. While the two can look very similar, the dementia symptoms occur before motor symptoms in Lewy body dementia, and in Parkinson's disease the reverse is true. 

"If you look at the brain, it's difficult to distinguish them," Dr. Litvan says. "But clinically, they are different."

What are the signs and symptoms of Parkinson's disease dementia?

Parkinson's disease dementia can't be diagnosed conclusively by a single test. Instead, doctors may use multiple tests and consider a range of Parkinson's disease dementia criteria, including symptoms like:

  • Feelings of disorientation or confusion
  • Agitation or irritability
  • Hallucinations (seeing, hearing, or feeling things that aren't real)
  • Delusions, characterized by paranoid thinking or suspicion
  • Visual-perceptual problems
  • Trouble coming up with words (lots of "tip of the tongue" moments)
  • Misnaming objects
  • Difficulty understanding complex sentences. 

Early symptoms of Parkinson's disease dementia generally aren't as obvious, though. It could start with mild cognitive problems, like changes to a person's executive function and ability to plan and multi-task. Individuals may have trouble managing appointments, paying bills, or weighing options when presented with a choice. They may also have trouble focusing during a conversation, making it difficult for them to function in certain social settings. 

Not all cases of cognitive impairment are severe—some people with Parkinson's disease can still manage their work and personal life just fine. But once a person has Parkinson's disease dementia, it usually means that they can no longer go about their daily life as they once did. 

What causes Parkinson's disease dementia?

Doctors don't yet know the exact cause of Parkinson's disease dementia, but they think it has to do with an accumulation of a protein called alpha-synuclein. When it builds up in the brain, it can create clumps called "Lewy bodies" in nerve cells, causing them to die.

The death of those cells usually results in the motor symptoms typically associated with Parkinson's disease. As Parkinson's disease progresses, those Lewy bodies may eventually damage the brain and cause problems with memory and thinking.

While many people with Parkinson's disease experience cognitive changes, not all of them will go on to develop dementia. It's estimated that between 50% and 80% of individuals with the disease eventually develop Parkinson's disease dementia, usually in the later stages of the disease.

What's the difference between memory loss and Parkinson's dementia?

Alzheimer's dementia and Parkinson's disease can both affect a person's memory, but not in the same way.

Generally speaking, Parkinson's dementia is not associated with the sort of memory loss that comes with Alzheimer's, the most common form of dementia. Put differently: It doesn't typically impact a person's ability to absorb and store new memories or information the way Alzheimer's does. 

"You can learn [with Parkinson's dementia], but it's difficult to retrieve the information that you have in your brain," Irene Litvan, MD, director of the Movement Disorder Center at the University of California, San Diego, tells Health. "You may not know where the cassette is, but if somebody asks you, 'Where were you when you lost it?' You can say, 'Oh, I was there.' " 

But that's not to say Parkinson's disease dementia doesn't affect memory at all. On the contrary, some people with Parkinson's dementia do indeed experience short- and long-term memory loss. They might also forget how to perform simple tasks, like how to run the dishwasher. And since Parkinson's can affect people in different ways, there's no way to tell whether someone with the disease will experience memory loss related to dementia.

Who gets Parkinson's disease dementia?

No two cases of Parkinson's are exactly alike, so it's hard to say for sure who will develop Parkinson's disease dementia and who will not. However, researchers have identified several factors that may increase a person's risk for Parkinson's disease dementia, including:

  • Older age, especially at the time Parkinson's symptoms began
  • Being a man
  • Advancing to late-stage Parkinson's disease
  • Experiencing visual hallucinations
  • More severe motor symptoms
  • Having a history of dementia in your family

People with Parkinson's disease may wish to consider planning for their future sooner rather than later, especially if they have certain risk factors or notice cognitive changes. That way, if their cognitive symptoms progress, their advance planning can help dementia caregivers (who have been struggling during the pandemic) best fulfill their wishes.

People usually live an average of five to seven years with the disease, but the prognosis of Parkinson's disease dementia can vary from person to person.

What's the treatment for Parkinson's disease dementia?

Given the symptoms, dementia is considered one of the most destructive non-motor symptoms of Parkinson's disease. While there's no cure for the condition, medications are available to help manage symptoms of Parkinson's disease dementia and improve a person's quality of life.

A doctor may also recommend making lifestyle changes, such as practicing sleep hygiene, eating a balanced diet, exercising, and avoiding alcohol, to help boost brain health and overall wellbeing.

If a loved one with Parkinson's disease is showing signs of dementia, get in touch with their doctor for a proper diagnosis.

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