Illegal drugs or alcohol did not play a role in Robin Williams' suicide, according to an autopsy report released last week, although doctors may have discovered another contributing factor: According to documents released by the Marin Country Coroner's office, Williams was suffering not just from early Parkinson's disease at the time of his death, but his brain also showed evidence of Lewy body disease—a progressive form of dementia that can cause confusion, movement difficulties, and hallucinations.

Lewy body disease is the second most common form of dementia, although it is often missed or misdiagnosed because its symptoms can mimic or occur along with Parkinson's or Alzheimer's disease, according to the National Institutes of Health. Radio personality Casey Kasem, who died earlier this year, had Lewy body disease, along with an estimated 1.3 million other Americans.

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"Patients with Lewy body disease frequently have emotionally laden hallucinations. They may think someone's out to get them, and they can suffer from fear, anxiety, and anger because of it," says Carol Lippa, M.D., director of the Clinical Memory Disorders Program at Drexel University, who did not treat Williams.

Reports that Williams' suicide could be linked to the disease are speculation at this point. TMZ reported this week that the actor, who was diagnosed with Parkinson's disease and depression before his death, had complained to his wife about how his Parkinson's medication made him feel, plus the coroner's report noted "a recent increase in paranoia." But there's no indication that he had been diagnosed with Lewy body disease or suffered from any obvious signs of the condition before he died.

“The use of the term dementia in the neuropathology report should not be inferred to mean that dementia was observed during life,” said Dennis Dickson, M.D., a neurologist at the Mayo Clinic in Jacksonville, Florida, in a statement released Monday by the Lewy Body Dementia Association, Inc. (Dr. Dickson, a member of the LBDA Scientific Advisory Council, did not treat Williams, either.) The statement also notes, however, that it is not unusual for early signs of dementia to go undetected.

Along with seeing and hearing people, animals, or objects that aren't there, people with Lewy body disease tend to have problems with attention and complex thoughts. (It differs from Alzheimer's disease in that memory loss is not its central feature.) They may also experience muscle stiffness and movement problems often attributed to Parkinson's disease.

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"You can develop Lewy body disease with or without Parkinson's, although they do often overlap," says Dr. Lippa. Depression is frequently present in patients with either condition, as well, although doctors don't know whether it's a risk factor for brain disease or an early symptom.

"Many people have mood problems long before they have signs of Parkinson's or dementia, so it's hard to tell whether a depressed person is more likely to get these diseases or whether they're already exhibiting one of the first signs," says Dr. Lippa. (Some forms of dementia tend to run in families, she adds, but this type seems to be mostly random.)

To further complicate the relationship between these conditions, people with Lewy body disease can have severe side effects to Parkinson's treatments. "The medications can make cognitive and emotional problems worse," Dr. Lippa says. "When something happens with a patient's emotional state, we have to determine whether it's because of a change in their medication or whether it's the disease progressing and affecting their mood."

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If you suspect that yourself or a loved one might be suffering from Lewy body disease, start by relaying your concerns to a primary care physician, Dr. Lippa says. If you don't get answers there, a neurologist, geriatrician, or psychiatrist may be able to help. "A lot of primary care doctors still aren't comfortable enough with the different forms of dementia to distinguish between them, so a specialist may be necessary."

Getting a proper diagnosis is important, she adds, because different types of dementia—as well as other conditions that can mimic dementia—are treated differently, and the wrong medications may make things worse, not better.

While Williams' death was tragic, Dr. Lippa says that one silver lining may be that more people will learn about Lewy body disease and hopefully seek help if they need it. "It's not an uncommon type of dementia, and so the more people are aware of it the better handle we can get on it."

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