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Lewy Body Dementia and Parkinson Disease Dementia

By Juebin Huang, MD, PhD

Lewy body dementia is progressive loss of mental function characterized by the development of Lewy bodies in nerve cells. Parkinson disease dementia is loss of mental function characterized by the development of Lewy bodies in people who have Parkinson disease.

  • People with Lewy body dementia fluctuate between alertness and drowsiness and may have difficulty drawing, hallucinations, and difficulty moving that is similar to that due to Parkinson disease.

  • Parkinson disease dementia typically develops about 10 to 15 years after other symptoms of Parkinson disease.

  • Diagnosis is based on symptoms.

  • Strategies are used to prolong functioning as long as possible, and the drugs used to treat Alzheimer disease may help.

Lewy body dementia is the third most common type of dementia. Lewy body dementia usually develops in people older than 60.

About 40% of people with Parkinson disease develop Parkinson disease dementia. The dementia usually develops after age 70 and about 10 to 15 years after Parkinson disease is diagnosed.

Dementia is a slow, progressive decline in mental function including memory, thinking, judgment, and the ability to learn. Dementia differs from delirium, which is characterized by an inability to pay attention, disorientation, an inability to think clearly, and fluctuations in the level of alertness.

  • Dementia affects mainly memory, and delirium affects mainly attention.

  • Dementia typically begins gradually and has no definite beginning point. Delirium begins suddenly and often has a definite beginning point.

Changes in the brain

In Lewy body dementia and Parkinson disease dementia, abnormal round deposits of a protein (called Lewy bodies) form in nerve cells. Lewy bodies result in the death of nerve cells.

In Lewy body dementia, Lewy bodies form throughout the outer layer of the brain (gray matter, or cerebral cortex). The cerebral cortex, which is the largest part of the brain, is responsible for thinking, perceiving, and using and understanding language.

In Parkinson disease dementia, Lewy bodies tend to form in part of the brain called the substantia nigra, the part that is affected in Parkinson disease. The substantia nigra is located deep within the brain stem and helps make movements smooth.

Lewy body dementia and Parkinson disease dementia seem to be variations of the same disorder. In this disorder, synuclein (a protein in the brain that helps nerve cells communicate) changes shape (misfolds) and slowly accumulates mostly in the brain but also in the digestive tract and heart. These abnormal deposits of synuclein are called Lewy bodies. The misfolded synuclein in Lewy bodies triggers more synuclein to misfold, resulting in the formation of more Lewy bodies. Brain damage results from the accumulation of Lewy bodies. Misfolded proteins that cause brain damage in this way are called prions. Prions cause brain disorders such as Creutzfeld-Jacob disease.

Lewy bodies also develop in some people with Alzheimer disease, although neurofibrillary tangles and senile plaques seem to be the main source of damage. Neurofibrillary tangles and senile plaques, typical in Alzheimer disease, sometimes develop in people with Lewy body dementia. Lewy body dementia, Parkinson disease dementia, and Alzheimer disease overlap considerably, and more research is needed to clarify their relationships.


Lewy body dementia

The symptoms of Lewy body dementia are very similar to those of Alzheimer disease. They include memory loss, disorientation, and problems remembering, thinking, understanding, communicating, and controlling behavior. But Lewy body dementia can be distinguished by the following:

  • In the early stages, mental function fluctuates, often dramatically, over a period of days to weeks but sometimes from moment to moment. One day, people may be alert and able to pay attention and converse coherently, and the next day, they may be drowsy, inattentive, and almost mute. People may stare into space for long periods.

  • At first, attention and alertness may be more impaired than memory, including memory for recent events. Memory problems may result more from lack of attention than from actual problems remembering.

  • The ability to copy and draw may be impaired more severely than other brain functions.

  • Psychotic symptoms, such as hallucinations, delusions, and paranoia, are more common in Lewy body dementia, and hallucinations tend to occur earlier.

In Lewy body dementia, hallucinations are usually visual ones, which are often complex and detailed. They may include recognizable animals or people. The hallucinations are often threatening. Over half of people with Lewy body dementia have complex, bizarre delusions. Instead of relieving these symptoms, antipsychotic drugs often make them and other symptoms worse or have other severe, sometimes life-threatening side effects (see Table: Antipsychotic drugs).

Like people who have Parkinson disease, people with Lewy body dementia have stiff muscles, move slowly and sluggishly, shuffle when they walk, and stoop over. Balance is easily lost, making falls more likely. Tremor also develops, but it usually develops later and causes fewer problems than it does in Parkinson disease. Problems with thinking and problems with muscles and movement usually begin within 1 year of each other.

Sleep problems are common. Many people with Lewy body dementia have rapid eye movement (REM) sleep behavior disorder. People with this disorder act out their dreams, sometimes injuring their bed partner.

The autonomic nervous system may malfunction, preventing the body from regulating internal functions, such as blood pressure and body temperature. As a result, people may faint, sweat too much or too little, have a dry mouth, or have urinary problems or constipation.

After symptoms appear, people usually live about 6 to 12 years.

Parkinson disease dementia

In Parkinson disease dementia (unlike in Lewy body dementia), mental function typically begins to deteriorate about 10 to 15 years after problems with muscles and movement appear.

As in other dementias, many mental functions can be affected. Memory is impaired, and people have difficulty paying attention and processing information. People think more slowly. Problems with planning and doing complex tasks occur earlier and are more common than in Alzheimer disease.

Hallucinations and delusions are less common and/or less severe than in Lewy body dementia.


  • A doctor's evaluation

  • Computed tomography or magnetic resonance imaging

Doctors must determine whether a person has dementia and, if so, whether the dementia is Lewy body dementia or Parkinson disease dementia.

Diagnosis of dementia

A diagnosis of dementia is based on the following:

  • Symptoms, which are identified by asking the person and family members or other caregivers questions

  • Results of a physical examination

  • Results of a mental status test

  • Results of additional tests, such as computed tomography (CT) or magnetic resonance imaging (MRI)

The mental status test, consisting of simple questions and tasks, helps doctors determine whether people have dementia.

More detailed testing (called neuropsychologic testing) is sometimes needed. This testing covers all the main areas of mental function, including mood, and usually takes 1 to 3 hours. This testing helps doctors distinguish dementia from age-associated memory impairment, mild cognitive impairment, and depression.

Information from the above sources helps doctors usually rule out delirium as the cause of symptoms (see Table: Comparing Delirium and Dementia). Doing so is essential because delirium, unlike dementia, can often be reversed if promptly treated.

Distinguishing delirium from Lewy body dementia is particularly important because in both, mental function also fluctuates.

Diagnosis of Lewy body dementia and Parkinson disease dementia

Doctors base the diagnosis of Lewy body dementia on its characteristic symptoms. Lewy body dementia is likely if mental function fluctuates in people who have visual hallucinations and muscle and movement symptoms similar to those caused by Parkinson disease.

Computed tomography (CT) and/or magnetic resonance imaging (MRI) may be done to rule out other causes of dementia.

A special type of CT called single-photon emission CT (SPECT) can help doctors diagnose Lewy body dementia.

Distinguishing Lewy body dementia from Parkinson disease dementia can be difficult because symptoms are similar:

  • Generally, Lewy body dementia is more likely if movement and muscle problems develop at the same time or shortly after mental function starts to decline.

  • Parkinson disease dementia is more likely if mental decline occurs years after muscle and movement problems develop in people with Parkinson disease and if muscle and movement symptoms are more severe than mental impairment.


  • Safety and supportive measures

  • Drugs used to treat Alzheimer disease

Treatment of Lewy body dementia and Parkinson disease dementia involves general measures to provide safety and support, as for all dementias.

Safety and supportive measures

Creating a safe and supportive environment can be very helpful (see Creating a Beneficial Environment for People With Dementia).

Generally, the environment should be bright, cheerful, safe, stable, and designed to help with orientation. Some stimulation, such as a radio or television, is helpful, but excessive stimulation should be avoided.

Structure and routine help people stay oriented and give them a sense of security and stability. Any change in surroundings, routines, or caregivers should be explained to people clearly and simply.

Following a daily routine for tasks such as bathing, eating, and sleeping helps people with dementia remember. Following a regular routine at bedtime may help them sleep better.

Activities scheduled on a regular basis can help people feel independent and needed by focusing their attention on pleasurable or useful tasks. Such activities should include physical and mental activities. Activities should be broken down in small parts or simplified as the dementia worsens.


The same drugs used to treat Alzheimer disease, particularly rivastigmine, may be used to treat Lewy body dementia and Parkinson disease dementia. These drugs may improve mental function.

Drugs used to treat Parkinson disease may help relieve the symptoms of Parkinson disease in both dementias (see Table: Drugs Used to Treat Parkinson Disease). However, in Lewy body dementia, these drugs may worsen confusion, hallucinations, and delusions.

In Lewy body dementia, antipsychotic drugs are not used to treat hallucinations and delusions if possible. These drugs tend to worsen muscle and movement symptoms.

Care for caregivers

Caring for people with dementia is stressful and demanding, and caregivers may become depressed and exhausted, often neglecting their own mental and physical health. The following measures can help caregivers (see Table: Caring for Caregivers):

  • Learning about how to effectively meet the needs of people with dementia and what to expect from them : Caregivers can get this information from nurses, social workers, organizations, and published and online materials.

  • Seeking help when it is needed: Caregivers can talk to social workers (including those in the local community hospital) about appropriate sources of help, such as day-care programs, visits by home nurses, part-time or full-time housekeeping assistance, and live-in assistance. Counseling and support groups can also help.

  • Caring for self: Caregivers need to remember to take care of themselves. They should not given up their friends, hobbies, and activities.

End-of-life issues

Before people with Lewy body dementia or Parkinson disease dementia become too incapacitated, decisions should be made about medical care, and financial and legal arrangements should be made. These arrangements are called advance directives. People should appoint a person who is legally authorized to make treatment decisions on their behalf (a health care proxy). They should discuss their health care wishes with this person and their doctor. Such issues are best discussed with all concerned long before decisions are necessary.

As the dementia worsens, treatment tends to be directed at maintaining the person’s comfort rather than at attempting to prolong life.

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