Parkinson’s Dementia: Signs and Stages

The disease is also associated with a decline in acetylcholine, a neurotransmitter that’s important for memory, Liang says.

In patients who have more serious dementia, the buildup of alpha-synuclein proteins (also called Lewy bodies) in areas of the brain that are important for memory, thinking or language is likely to blame, says Michael Okun, M.D., medical adviser to the Parkinson’s Foundation and director of the Norman Fixel Institute for Neurological Diseases at University of Florida Health.

Tau and amyloid beta, two proteins linked with Alzheimer’s, may also play a role in Parkinson’s dementia. For some people with Parkinson’s, Liang says, “on autopsy, there is mixed pathology…. There’s amyloid and tau, as well as Lewy bodies.”

Who is at risk?

Not everyone with Parkinson’s faces an equal risk of memory trouble. Those who develop cognitive impairment tend to be older and have been living with the disease for longer.

At any given moment, about 25 percent of people with Parkinson’s disease have some form of dementia, ranging from very mild to more severe. Among people who’ve had Parkinson’s for 20 years or more, as many as 80 percent may have dementia.

But neither older age nor longer time since diagnosis guarantees that dementia will develop. “We have a group of people with Parkinson’s that we call ‘cognitive superstars,’ ” Okun says. “We keep testing them year after year, and they score very well in memory and cognitive domains. The point is that there’s wide variation.”

He’s referring to the specific symptoms a person with Parkinson’s will develop, how severe they’ll be and how quickly the disease will progress. That’s true of motor as well as cognitive symptoms.

The Parkinson’s Progression Markers Initiative (PPMI), a study led by the Michael J. Fox Foundation for Parkinson’s Research, has been tracking thousands of people with Parkinson’s, or who are at high risk for the disorder, since 2010. The study seeks answers to many questions, including who might be more likely to develop dementia.

In a 2024 study in npj Digital Medicine, researchers, including Okun, used AI to analyze data on 406 people in the PPMI cohort with newly diagnosed Parkinson’s to classify three subtypes of the disease: slow, moderate and rapid pace. Pace of disease directly correlated with the severity of symptoms at disease onset. That is, slow pacers had the mildest symptoms, and severity increased from there.

Dementia was also more common in people with moderate and rapid pace disease.

The study also found several genes that seem to predispose a person to the rapid subtype. This knowledge may someday lead to more effective treatments, Liang says. “Ultimately, if we can understand why the neuronal [genetic] programs are altered so that certain cell populations are aging faster, we’ll have a better way to stall or slow or stop the progression.”

Specific symptoms might also tip off doctors about a patient’s dementia risk. “People who have resting tremor tend to progress more slowly,” Okun says. “If they’re going to get cognitive challenges or dementia, they get that later than people who may lack a tremor or who have … balance and walking problems.”

Using these symptoms as predictors for dementia risk isn’t foolproof, however, as symptoms can change over time.

REM sleep behavior disorder appears to raise the risk for depression, cognitive decline, dementia and hallucinations, according to a study reported in 2025 in npj Parkinson’s disease tracking 452 people with Parkinson’s. 

In REM sleep behavior disorder, people physically act out their dreams while sleeping, when the muscles should typically be paralyzed. The condition is a risk factor for Parkinson’s and potentially an early sign of disease onset.

How to reduce risk

You can take steps to lower the risk of memory problems or catch them as soon as possible.

“One of the biggest things you want to do to stall and prevent cognitive issues in general is exercise, exercise, exercise — physical exercise,” Liang says.

Even people who’ve developed substantial motor problems can find classes or activities that work for their level or are specifically for people with Parkinson’s. (Check out Rock Steady Boxing, Pedaling for Parkinson’s and Power for Parkinson’s, which offers seated exercise classes on YouTube.)

Experts also recommend maintaining strong social ties, good sleeping habits and a healthy, balanced diet — such as the Mediterranean, with its emphasis on anti-inflammatory fatty fish, whole foods and plenty of antioxidant-rich fruits and vegetables.

Challenge your brain, Okun says. “Do something with your left hand if you're right-handed,” he says. He also encourages patients to listen to audiobooks with a partner or caregiver, stopping after each chapter and having a discussion to ensure that both parties can reiterate what happened (if not, repeat the chapter).

If you’re experiencing memory problems, tell your medical provider right away. Your doctor should start by screening you for other conditions that mimic Parkinson’s-related memory loss, Okun says, including depression, thyroid disease, vitamin deficiencies and urinary tract infections.

“It’s exceedingly rare to get cognitive dysfunction that crosses over to dementia within the first few years of a Parkinson’s diagnosis,” he says. “If we see that, we actually suspect another form called Lewy body dementia.”

Your physician should also review all your medications because even seemingly innocuous over-the-counter drugs and supplements can be problematic. Benadryl (diphenhydramine), for instance, may cause cognitive problems because it blocks acetylcholine.

When in doubt, ask your doctor to refer you to a neuropsychologist for a full workup. Neuropsychological testing takes a few hours, but it should yield useful information about your mental status so that you can be properly treated and monitored. Depending on the results, your doctor may recommend that you work with an occupational therapist on organizational strategies or participate in a cognitive training program.

Your doctor may also prescribe Exelon (rivastigmine), a drug that may boost cognition by increasing the amount of acetylcholine in the brain.

Sometimes test results can simply give you peace of mind, Liang says. “It can be very reassuring to have some quick testing in the office that shows there is not as much of an issue as you suspected.”

Whatever your level of functioning, raise any questions you have about your memory with your neurologist. “Your doctor might focus on motor symptoms, but if you’re concerned, you should absolutely talk to your doctor and ask what you can do,” Dolhun says. “Be your best advocate.”