Hank: Here at SciShow we don't usually cover a lot of celebrity news unless we're talking about celebrity engineers, or celebrity scientists. When we do it's usually to explain something science-related that's happened in a celebrity's life. Today we're going to talk about Robin Williams, whose autopsy has shown that he was suffering from the early stages of a disease called Lewy body dementia.

This condition is debilitating and surprisingly common for something most people have never heard of. It's the second most common cause of dementia, after Alzheimer’s disease. It's also the most frequently misdiagnosed cause of dementia partly because it's often mistaken for Parkinson’s disease until the hallucinations start.

And that's exactly what happened to Robin Williams, who had been diagnosed with the early stages of Parkinson's at the time of his death, but his autopsy revealed small clusters known as Lewy bodies in his cerebral cortex, a typical sign of Lewy body dementia. Lewy bodies are small clumps of proteins mainly one called alpha-synuclein. Everyone has alpha-synuclein in their brains, as well as in other tissues like their hearts and muscles. It's found in nerve cells and appears to have something to do with the release of neurotransmitters, the chemicals that help nerves communicate with each other, although its role isn't really understood.

What we do know is that it's perfectly healthy to have alpha-synuclein in your body. Scientists still aren't sure what causes Lewy Body Dementia, but Lewy bodies seem to form when something like a mutation or damage to the gene responsible for making alpha-synuclein causes those protein molecules to be created in the wrong shape. And when alpha-synuclein is folded incorrectly, it can start to clump together. Those clumps become the Lewy bodies and they slowly accumulate spreading through the brain and interfering with the neurons ability to communicate with each other.

In Parkinson's, Lewy bodies form in the brain stem and the substantia nigra, the part of the brain that produces the neurotransmitter dopamine. Both of those areas help control muscle movement, so the result is a loss of coordination. All signals for muscle movement have to pass through your brain stem, and dopamine is a chemical that we've talked about before for its role in reward and addiction, but it's also part of what lets you make smooth uninterrupted movement. Damage to either or both of these regions leads to the tremors, stiffness, and difficulty in walking that are the most visible symptoms of Parkinson's disease.

So if the formation of Lewy bodies causes Parkinson's, then what makes Lewy body dementia a different disease and why haven't you heard of it? Well the answers to those questions turn out to be related. You probably haven't heard of it because we only zeroed in on the difference between Lewy Body dementia and Parkinson's in the 1990s, and it's misdiagnosed so frequently- as either Parkinson's or Alzheimer's disease, depending on the individual's symptoms- that it hasn't attracted much attention.

The difference between Lewy Body Dementia and Parkinson's comes from where those Lewy bodies form. The buildup of Lewy bodies during Parkinson's disease happens mainly in the brainstem. But in Lewy Body Dementia, those bodies form throughout the cerebral cortex, including sometimes in the substantia nigra, which can give Lewy body dementia some Parkinson's-like symptoms. Parkinson's is easier for doctors to diagnose because the brain stem is small and packed with all of our brain's simplest equipment, which we mostly understand. We know what it looks like when it stops working. And it helps that the Lewy bodies that form there are pretty large and therefore easy to see during an autopsy, which is useful for researchers.

We've known about them since 1912, when Doctor Friedrich Lewy discovered them in the brains of some people with Parkinson's disease. But in Lewy body dementia, the protein clumps are so small that until very recently, we couldn't detect them at all.  New methods for studying brain tissue allowed us to see Lewy bodies in other parts of the brain for the first time only in the 1990s.

But even if they're hard to see, having those protein clusters forming in brain cells everywhere gives Lewy Body Dementia a long list of symptoms that Parkinson's doesn't share, which is what doctors do use to diagnose it. Things like hallucinations, loss of spatial reasoning, sleep disorders, and cognitive and memory impairment, similar to Alzheimer's. According to statements from William's wife, and according to the autopsy report, Robin Williams was not suffering from any of those advanced symptoms at the time of his death. Lewy bodies accumulate slowly over years with gradually worsening symptoms.

So is there a cure, or at least a treatment? Well no, not yet. Lewy Body dementia is especially hard to treat because patients tend to have a severe sensitivity to many of the antipsychosis medications that doctors might prescribe to help manage the hallucinations. But we can hope that Robin Williams' diagnosis might help bring some awareness to these diseases.

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