Robin Williams' autopsy showed that he had Lewy Body Dementia. Lewy Body Dementia is a progressive dementia that involves the death of cells in the brain's outer layer and part of the mid-brain. The disease is very similar to Frontotemporal Degeneration which involves the degeneration of nerve cells in the frontal or temporal lobes of the brain. Lewy Body Dementia, like Frontotemporal Degeneration is frequently misdiagnosed as Parkinson's disease.