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What is Lewy body dementia?

Robin Williams speaks onstage during the 65th Annual Primetime Emmy Award in L.A.  Sept.22, 2013

Kevin Winter, Getty Images

A new report that emerged Tuesday about Robin Williams' death has put a spotlight on the second most commonly diagnosed type of dementia, but one that many people have never heard of.

Lewy body dementia, which affects about 1.3 million Americans, is a type neurodegenerative disease that has many attributes similar to both Parkinson's and Alzheimer's disease.

Memory and cognitive problems are some of the common symptoms of Lewy body dementia. But its disease processes are much more closely tied to Parkinson's disease. Parkinson's disease and Lewy body dementia are both caused by the buildup of small misfolded protein deposits in brain tissue known as alpha-synuclein. This is a different type of naturally-occurring protein than tau and amyloid plaques, which are the hallmark of Alzheimer's disease.

Williams' wife has said he was in "the early stages of Parkinson's disease" before he committed suicide on Aug. 11.

Lewy body dementia is "very complex and it requires treating a much broader range of symptoms to maximize quality of life," Angela Taylor, director of programs at the Lewy Body Dementia Association, told CBS News. Symptoms of the disease can include memory, cognitive and motor problems, muscle stiffness, gait problems and hallucinations. Currently there is no cure for Lewy body dementia, which means doctors must help patients manage each of these symptoms independently when they emerge.

Taylor added that the disease can be difficult to diagnose since there is not currently a medical test to differentiate Lewy body dementia from other types of dementia, such as Alzheimer's disease and vascular dementia. Many of the symptoms associated with Lewy body dementia can be similar to Alzheimer's disease. For example, a decline in cognitive abilities is one of the early signs of Alzheimer's disease; it's also associated with Lewy body dementia, but is not typically a symptom of Parkinson's disease.

This is why Lewy body dementia is also the most frequently misdiagnosed form of dementia. A survey conducted by Taylor's organization found Lewy body dementia patients spent an average of 18 months seeking medical evaluations and visited an average of three or more doctors before receiving a diagnosis.

"The report indicates that [Williams] was being treated for Parkinson's and that is one of the features of dementia with Lewy bodies," said Taylor. "Hallucinations are a core feature of Lewy body dementia."

Treatment for this type of dementia can be challenging. The antipsychotic medications used for patients with Alzheimer's to manage psychiatric problems often are not tolerated by people with Lewy body dementia. According to the Lewy Body Dementia Association, as many as 50 percent of Lewy body dementia patients placed on antipsychotic medications can experience a worsening of symptoms and the impact can even be fatal.

Experts say the distribution of telltale protein deposits in the brain tend to be limited in a person with Parkinson's disease. However, in a patient with Lewy body dementia, the proteins are spread widely throughout the brain. This detail most likely could only be uncovered through an autopsy.

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