The role of the Lewy body in idiopathic Parkinsonism.

We have explored the role of Lewy bodies in idiopathic Parkinsonism (IP) to determine whether they are linked to cell death, or to a reactive and protective process associated with cell survival. We start with a definition of IP that is not dependent upon the presence of Lewy bodies. We have derived a mathematical model that predicts the age-specific annual incidence rates of IP under the assumption that the disorder arises from the ;Incidental Lewy Body State' (ILBS). We have compared these predicted rates with the corresponding rates expected from our model assuming that IP develops in normal subjects. Both of these predictions were then matched against the observed age-specific incidence rates for IP. The predicted rates based upon the premise that ILBS is linked to IP yielded a far closer fit to the observed data. Our analysis indicates that ILBS is sufficient to account for all cases of IP. Our findings further suggest that ILBS may also predispose to other neurodegenerative disorders that are characterized by neuronal loss and the presence of Lewy bodies in various regions of the brain. Finally, we conclude that Lewy bodies are likely to be associated with neuronal death, rather than representing a reactive, protective response to cell damage.