An elderly man and woman stand next to each other, slightly overlapping. Red dots are sprinkled across the man's head, and blue dots are on the woman's.

Alzheimer's & Parkinson's Disease-Related Dementia: What's the Difference?

As we or our loved ones age, we may be prone to memory loss and confusion. These problems can be due to many different underlying conditions that affect the brain and impair its functioning. Both Alzheimer’s and Parkinson’s diseases can disrupt the way the brain processes. Both conditions may lead to memory loss, confusion, and problems thinking and managing day-to-day life. Together, these kinds of symptoms are known as dementia.

How can you tell the difference between Alzheimer’s and Parkinson’s disease-related dementia? For starters, Parkinson’s usually starts with movement problems. Dementia happens at a later stage, at least a year after diagnosis.1 When you have Alzheimer’s, on the other hand, the disease starts with memory loss and confusion.

Early signs and symptoms are different

Parkinson’s disease generally begins as a movement disorder. Early signs and symptoms include:2

  • Tremor, which often begins in the hand or fingers
  • Slowed movement, which may include foot dragging
  • Rigidity
  • Difficulty writing
  • Slowed automatic movements such as blinking, smiling, and swinging your arms when you walk

Alzheimer’s disease generally begins as noticeable memory loss. Early signs and symptoms include:3,4

Key brain changes are different

The key brain changes linked to Parkinson’s disease and Parkinson’s-related dementia are abnormal deposits of common brain proteins, called alpha-synuclein. These deposits are known as Lewy bodies, named after the doctor who discovered them. As more of these proteins clump in the brain, normal brain cells begin to die off.1

In Alzheimer’s disease, the key brain changes include the buildup of different brain proteins, called amyloid and tau. When amyloid proteins clump together, they form abnormal structures known as plaques. Abnormal groups of tau proteins form tangles.3 Over time, the buildup of these proteins causes normal brain cells to die, and affected parts of the brain may shrink.5

Symptoms related to brain function are different

There is some overlap, but in general, the overall cognitive symptoms that people experience with Parkinson’s disease dementia and Alzheimer’s are different. Alzheimer’s mainly affects language and memory at the outset, whereas Parkinson’s affects problem-solving, speed of thinking, memory, and mood.6

Unlike in Alzheimer’s disease, people with Parkinson’s-related dementia often experience hallucinations, delusions, and paranoid thoughts. Both conditions can lead to depression, anxiety, and sleep disturbances.4,6

Number of people affected

Parkinson’s disease is thought to affect about 2 percent of Americans over 65. Of those, about 50 to 80 percent will go on to develop Parkinson’s-related dementia.1 The Parkinson’s Foundation estimates that nearly 1 million Americans will be living with Parkinson’s by 2020. The disease affects 1.5 times more men than women.7

Approximately 5.8 million Americans are currently living with Alzheimer’s disease. That number is expected to increase to 14 million by 2050.8 There is little difference between numbers of men and women who develop Alzheimer’s, but there are more women with the disease, because women tend to live longer than men.3

Can you have both Parkinson’s and Alzheimer’s?

People who already have Parkinson’s disease and later develop signs of dementia are diagnosed with Parkinson’s dementia.6 However, if you first have Alzheimer’s disease and develop signs of movement difficulties, you can also have a diagnosis of Parkinson’s disease.

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