Controversy: is Parkinson's disease a single disease entity? Yes.

Parkinson's disease (PD) is a common, and in principle, sporadic, neurodegenerative disorder that occurs in adults. Pathological studies have revealed that in PD, nerve cell loss and Lewy bodies (LB) are distributed widely in the nervous system. Moreover, molecular pathology has made remarkable advances over the last several years, after the identification of alpha-synuclein gene abnormality in familial PD. Extensive pathological findings support the idea that PD is a single disease entity and that there are no cases of PD in which neurodegeneration occurs only in the substantia nigra and in which there are no LBs.