Does Parkinson's Disease Cause Dementia?

Many people with Parkinson's disease experience cognitive changes–such as difficulty planning and multitasking–but not all of them develop dementia. On average, Parkinson's disease dementia symptoms set in about 10 years after a person first starts having movement problems, according to a review published in the Journal of Neural Transmission.

Parkinson's disease is primarily known for the movement symptoms it causes, such as a resting tremor, stiffness, and balance and coordination difficulties, per the National Institute on Aging (NIA). The disease can also cause symptoms unrelated to movement, such as dementia, which may develop in up to 75% of people with Parkinson's disease, per the review in the Journal of Neural Transmission.

Getting a Parkinson's Disease Dementia Diagnosis

Dementia manifests differently from person to person, but the overarching indicator is cognitive impairment.

Parkinson's disease dementia (PDD) and dementia with Lewy bodies (DLB) are two separate neurological conditions that share many clinical, neurochemical, and morphological features. Both conditions are caused by abnormal protein deposits in the brain called Lewy bodies and occur mostly in people over 50 years old.

Dementia with Lewy bodies starts with mental symptoms such as hallucinations, loss of thinking abilities, and changes in attention and wakefulness. Movement symptoms occur later (within a year) and include muscle stiffness, slow movement, balance and coordination problems, and resting tremors, per the NIA.

Timing of dementia is the main factor that differentiates DLB from PDD. In DLB, thinking symptoms occur before motor symptoms or within a year from the start of motor symptoms. In PDD, motor symptoms come first. By the time people develop PDD, they've already had Parkinson's disease for some time.

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

If someone shows signs of dementia within a year of their Parkinson's disease diagnosis, it could be that they were misdiagnosed. They might have dementia with Lewy bodies instead.

Signs and Symptoms

PDD can't be diagnosed conclusively by a single test. Instead, healthcare providers may use multiple tests and consider a range of criteria, including mental symptoms such as, per the NIA and Parkinson's Foundation:

• Hallucinations (seeing, hearing, or feeling things that aren't real)
• Concentration, attention, alertness, and wakefulness changes that occur day-to-day or throughout the day
• Feelings of disorientation or confusion
• Agitation or irritability
• 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 PDD generally aren't as obvious, though. It could start with mild cognitive problems, such as changes to a person's executive function and ability to plan and multitask. At first, people may have trouble managing appointments, paying bills, making decisions, or focusing during a conversation.

Causes

Experts don't know exactly what causes PDD but believe an accumulation of a protein called alpha-synuclein may play a role in the condition. When alpha-synuclein builds up in the brain, it can create clumps called "Lewy bodies" in neurons (nerve cells), causing the neurons to die, per the NIA.

The death of those cells usually results in the movement symptoms typically associated with Parkinson's disease. As Parkinson's disease progresses, those Lewy bodies may eventually damage more of 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. Those that do are usually in the later stages of the disease and have had Parkinson's disease for 10 years.

What's the Difference Between Memory Loss and Parkinson's Dementia?

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

Generally speaking, PDD is not associated with the sort of memory loss that comes with Alzheimer's disease. PDD 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, told 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.'"

That's not to say PDD doesn't affect memory. Some people with Parkinson's dementia do indeed experience short- and long-term memory loss. They might forget how to perform simple tasks, such as how to run the dishwasher. And since Parkinson's disease can affect people in different ways, there's no way to tell whether someone with Parkinson's disease will experience memory loss.

Risk Factors

No two cases of Parkinson's are exactly alike, so it's hard to say who will or won't develop PDD. However, researchers have identified several factors that may increase a person's risk for PDD, including:

• Older age
• Being a man
• Experiencing visual hallucinations
• Having more severe motor symptoms, especially non-tremor symptoms
• Smoking and hypertension
• Having a history of dementia in your family
• Advancing to late-stage Parkinson's disease

Although it may be stressful, if you have Parkinson's disease, it may benefit you to be proactive and come up with a plan for your care before you notice any cognitive changes. This way, if you develop cognitive symptoms, dementia caregivers can use your advance planning to best fulfill your wishes.

People with PDD usually live an average of four years with the disease, but the prognosis can vary from person to person, per the December 2017 review.

Treatment

Dementia is considered one of the most destructive nonmotor symptoms of Parkinson's disease, per a September 2014 paper in the journal Neurology. While there's no cure for the condition, medications are available to help manage some symptoms of PDD and improve a person's quality of life. Treatment may work for a limited time, per the NIA.

Physical, speech, and occupational therapy may be helpful, as well as mental health and palliative care–a type of care that provides support for serious illnesses.

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

If you or a loved one has Parkinson's disease and are noticing cognitive changes, reach out to your healthcare provider to get a proper diagnosis and support.