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.
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 (see see Parkinson's Disease) develop Parkinson disease dementia. The dementia usually develops after age 70 and about 10 to 15 years after Parkinson disease is diagnosed.
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.
Whether Lewy body dementia and Parkinson disease dementia are distinct disorders or variations of the same problem is unclear. 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 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 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.
Doctors base the diagnosis on 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. Doctors must rule out delirium, which requires prompt treatment, because in delirium, mental function also fluctuates. Computed tomography (CT) and magnetic resonance imaging (MRI) may be done to rule out other causes of 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.
Treatment involves general measures to provide safety and support, as for all dementias (see Treatment).
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. 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.
Last full review/revision July 2013 by Juebin Huang, MD, PhD