Parkinson's Dementia vs. Dementia With Lewy Bodies

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Have you ever wondered if there was any difference between dementia with Lewy bodies and Parkinson's disease dementia? If you've ever heard the symptoms of these two disorders, they sound surprisingly alike. That's because they're both types of Lewy body dementia: dementia with Lewy bodies (DLB) and Parkinson's disease dementia (PDD).

Illustration of a neuron with Lewy bodies
Dr_Microbe / Getty Images

Shared Symptoms

To understand the difference between PDD and DLB, it's important to understand that there are two sets of symptoms that occur in both PDD and DLB.

  • Body: Symptoms that affect the body include muscle weakness, rigidity (stiffness) and slowness in movements.
  • Brain: Symptoms evident in the brain include impaired executive functioning, attention span, and memory loss.

Both of these types of dementia have symptoms that affect the body and the brain. Hallucinations and depression are often present in both types of dementia, as well. Both conditions are often treated by medications typically prescribed for Parkinson's disease, such as carbidopa-levodopa (Sinemet), which may be helpful by improving the ability to move and physically function, as well as cholinesterase inhibitor medications, which may slow down the cognitive decline.

Differences Between PDD and DLB

So, how are PDD and DLB different from each other? That depends on whom you ask. Some clinicians feel that these two conditions are simply different versions of the same disorder. In fact, some professionals use the terms interchangeably. Yet, according to currently agreed-upon diagnostic guidelines, there are some differences.

Onset of Symptoms

The biggest difference between Parkinson's disease dementia and dementia with Lewy bodies is the order of onset of the symptoms. Clinicians usually distinguish between these by asking which set of symptoms (body or brain) appeared first.

To diagnose Parkinson's disease dementia, the motor and movement symptoms, including rigidity, weakness, and tremors, should be present at least one year before cognitive declines develop.

Dementia with Lewy bodies is diagnosed if the symptoms in mobility and muscle weakness occur at the same time as a cognitive decline, if the cognitive symptoms occur before the motor symptoms, or if a cognitive decline develops less than one year after the motor symptoms begin.

Variation in Cognition

People who have dementia with Lewy bodies tend to exhibit greater variation in cognitive ability than those with Parkinson's disease dementia. This is important to understand because family members and caregivers may otherwise become frustrated and believe that the individual is choosing the timing of (or even faking) his cognitive impairments.

Understanding the possible fluctuations in mental abilities is also important in cognitive testing and evaluation. Persons with Parkinson's disease dementia may perform similarly on cognitive tests even if you assess them at different times of the day or on different days. However, a person who has dementia with Lewy bodies may show improved memory or concentration at times and notably worsened cognition at other times. Thus, it's important to conduct a cognitive assessment more than once to accurately evaluate an individual who has dementia with Lewy bodies.

Sleep Habits

DLB often affects sleep more significantly because REM sleep disorder, a condition where people physically act out their dreams as they sleep, is more common in the early stages of DLB as compared to PDD. This is often a surprising early sign of Lewy body dementia.


Both types of dementia are characterized by the presence of Lewy bodies in the brain, atrophy of brain cells and acetylcholine transmitter problems. Both types of dementia (although this may be more common in DLB) may also have some amount of amyloid beta protein deposits in the brain as well, which is one characteristic of Alzheimer's disease.

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By Esther Heerema, MSW
Esther Heerema, MSW, shares practical tips gained from working with hundreds of people whose lives are touched by Alzheimer's disease and other kinds of dementia.