Parkinson's disease dementia is an impairment in thinking and reasoning that eventually affects many people with Parkinson's disease.

About Parkinson's disease dementia

The brain changes caused by Parkinson's disease begin in a region that plays a key role in movement. As Parkinson's brain changes gradually spread, they often begin to affect mental functions, including memory and the ability to pay attention, make sound judgments and plan the steps needed to complete a task.

The key brain changes linked to Parkinson's disease and Parkinson's disease dementia are abnormal microscopic deposits composed chiefly of alpha-synuclein, a protein that's found widely in the brain but whose normal function isn't yet known. The deposits are called "Lewy bodies."

Lewy bodies are also found in several other brain disorders, including dementia with Lewy bodies (DLB). Evidence suggests that dementia with Lewy bodies, Parkinson's disease and Parkinson's disease dementia may be linked to the same underlying abnormalities in brain processing of alpha-synuclein.

Another complicating factor is that many people with both dementia with Lewy bodies and Parkinson's disease dementia also have plaques and tangles — hallmark brain changes linked to Alzheimer's disease.

Parkinson's disease is a fairly common neurological disorder in older adults, estimated to affect nearly 2 percent of those older than age 65. The Parkinson's Foundation estimates that 1 million Americans have Parkinson's disease. It is estimated that 50 to 80 percent of those with Parkinson's disease eventually experience Parkinson's disease dementia. The average time from onset of Parkinson's to developing dementia is about 10 years. Sign up for our e-news to receive updates about Alzheimer’s and dementia care and research.

Learn more: Dementia with Lewy Bodies, Mixed Dementia.


Parkinson's disease dementia is a decline in thinking and reasoning that develops in someone diagnosed with Parkinson's disease at least a year earlier. Common symptoms include:

  • Changes in memory, concentration and judgment.
  • Trouble interpreting visual information.
  • Muffled speech.
  • Visual hallucinations.
  • Delusions, especially paranoid ideas.
  • Depression.
  • Irritability and anxiety.
  • Sleep disturbances, including excessive daytime drowsiness and rapid eye movement (REM) sleep disorder.


As with other types of dementia there is no single test — or any combination of tests — that conclusively determines that a person has Parkinson's disease dementia.

Many experts now believe that Parkinson's disease dementia and dementia with Lewy bodies are two different expressions of the same underlying problems with brain processing of the protein alpha-synuclein. But most experts recommend continuing to diagnose dementia with Lewy bodies and Parkinson's dementia as separate disorders.

Guidelines for diagnosing Parkinson's disease dementia and dementia with Lewy bodies are:

  • The diagnosis is Parkinson's disease dementia when a person is originally diagnosed with Parkinson's based on movement symptoms and dementia symptoms don't appear until a year or more later.
  • The diagnosis is dementia with Lewy bodies when:
    • Dementia symptoms appear within one year after movement symptoms.
    • Both dementia symptoms and movement symptoms are present at the time of diagnosis.
    • Movement symptoms develop within a year of a dementia with Lewy bodies diagnosis.

Brain imaging

Since individuals with Parkinson's are at high risk for dementia as their disease progresses, doctors monitor those with Parkinson's closely for signs of thinking changes. When someone with Parkinson's develops thinking changes, doctors often order magnetic resonance imaging (MRI) of the brain to rule out tumors, structural changes and evidence for vascular disease.

Causes and risks

Certain factors at the time of Parkinson's diagnosis may increase future dementia risk, including older age, greater severity of motor symptoms, and having mild cognitive impairment (MCI).

Additional risk factors may include:

  • Hallucinations in a person who doesn't yet have other dementia symptoms.
  • Excessive daytime sleepiness.
  • Parkinson's symptom pattern known as postural instability and gait disturbance (PIGD), which includes "freezing" in mid-step, difficulty initiating movement, shuffling, problems with balance and falling.

Treatment and outcomes

There are no treatments to slow or stop the brain cell damage caused by Parkinson's disease dementia. Current strategies focus on helping symptoms.

If your treatment plan includes medications, it's important to work closely with your physician to identify the drugs that work best for you and the most effective doses. Treatment considerations involving medications include the following issues:

  • Cholinesterase inhibitors drugs are the current mainstay for treating thinking changes in Alzheimer's. They also may help Parkinson's disease dementia symptoms.
  • Antipsychotic drugs should be used with extreme caution in Parkinson's disease dementia. Although physicians sometimes prescribe these drugs for behavioral symptoms that can occur in Alzheimer's, they may cause serious side effects in as many as 50 percent of those with Parkinson's disease dementia and dementia with Lewy bodies. Side effects may include sudden changes in consciousness, impaired swallowing, acute confusion, episodes of delusions or hallucinations, or appearance or worsening of Parkinson's symptoms.
  • L-dopa may be prescribed to treat Parkinson's movement symptoms. However, it can sometimes aggravate hallucinations and confusion in those with Parkinson's dementia or dementia with Lewy bodies.
  • Antidepressants may be used to treat depression, which is common in both Parkinson's disease dementia and dementia with Lewy bodies. The most commonly used antidepressants are selective serotonin reuptake inhibitors (SSRIs).
  • Clonazepam may be prescribed to treat REM sleep disorder.

Like other types of dementia that destroy brain cells, Parkinson's disease and Parkinson's disease dementia get worse over time and speed of progression can vary.

Help is available

The Alzheimer's Association can help you learn more about Alzheimer's disease and other dementias, and help you find local support services. Call our 24/7 Helpline at 800.272.3900.

Michael J. Fox Foundation for Parkinson's Research website offers information for people living with Parkinson's disease and research updates.

Parkinson's Foundation is a nonprofit organization providing information and resources for diagnosed individuals, families and health professionals. Call the Parkinson's Foundation at 800.473.4636.