Wikipedia says causes aren’t really known. The lewy bodies are plaques that build up in the brain, similar to Parkinson’s disease. Given that, it doesn’t seem as likely.
According to the wiki article on Dementia with Lewy bodies, one of the symptoms is “blank expression (reduced range of facial expression)”, which could account for his appearence in that picture.
For such a physical comedian, with such an active face as part of his humour, that would be a very sad possibility.