Dementia is a progressive (gradually worsening) decline of mental abilities that disturbs "cognitive" functions such as memory, thought processes, and speech as well as behavior and movements.
Dementia with Lewy bodies (DLB) is the name for a group of disorders in which dementia is caused by the presence of Lewy bodies in the brain. Lewy bodies are small round clumps of normal proteins that -- for unknown reasons -- become abnormally clumped together inside neurons (brain cells). Whether the Lewy bodies directly cause gradual damage to the brain cells, impairing their function and eventually killing them, or are only a marker of some other destructive process is not known.
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Lewy bodies are named after Frederich Lewy, the doctor who first described them in 1912. Dr. Lewy first found Lewy bodies in the brains of people with Parkinson's disease. Parkinson's disease is a condition best known for disrupting body movements. The most common of these "motor" symptoms are tremor (shaking or trembling) of the hands (that mainly occurs when the hands are at rest and not moving), rigidity (stiffness) of the trunk and limbs, slowness of movement, and loss of balance and coordination. Estimates vary from 30% to 60% of people with Parkinson's disease develop dementia.
Scientists later discovered cases of Alzheimer's-type dementia linked to Lewy bodies. This was thought to be very rare, but as tests of brain tissue improved, it became clear that Lewy bodies were fairly common and were linked to several different types of dementia. A type of dementia similar to but different from Alzheimer's disease was recognized and called dementia with Lewy bodies, or DLB. DLB is now believed to be the second or third most common type of dementia after Alzheimer's disease, accounting for about 10% to 20% of all dementias. (There is controversy about whether DLB or vascular dementia is the second most common form of dementia.)
The relationship between DLB and Parkinson's disease is not completely understood. When motor symptoms appear first and predominate over cognitive symptoms, the diagnosis is believed to be Parkinson's disease. When cognitive impairment and behavioral disturbances are prominent early symptoms, DLB is believed to be the diagnosis.
DLB is a disease of aging. People affected by DLB are usually elderly or in late middle age.
Causes of Dementia With Lewy Bodies
We do not know why Lewy bodies form in the brain.
Symptoms of Dementia With Lewy Bodies
DLB symptoms vary from person to person. The one characteristic common to everyone with DLB is progressive loss of mental abilities that interferes with everyday activities. This may include the following:
Loss of recent memory
Inability to concentrate or pay attention
Difficulty thinking, reasoning, solving problems
Misperceptions of space and time
Mental function usually varies in DLB, getting better and worse over time. Although the sharpness of our mental function varies in everyone -- we all have our good moments and bad moments, or are "morning" persons or "evening" persons -- this fluctuation is especially dramatic in DLB. This is especially true of alertness and attention. A person with DLB typically has periods of being alert, coherent, and oriented that alternate with periods of being confused and less responsive. This usually is considered more characteristic of DLB than of other types of dementia. Other symptoms of DLB include:
Abnormal movements of Parkinson's disease (shuffling gait, tremor, muscle stiffness)
Sensitivity to "neuroleptic" drugs given to control hallucinations and delusions
None of these symptoms are unique to DLB or definitively point to DLB as a diagnosis. In fact, people with DLB often are very difficult to distinguish from those with Alzheimer's disease. People with DLB, however, often develop both the cognitive symptoms of dementia (e.g., problems with memory and attention similar to those seen in Alzheimer's Disease) and motor symptoms (such as those seen in Parkinson's Disease) within one year of each other.