There are three main considerations in the cause of Parkinson's disease (PD)—genetic, environmental, and environmental trigger in genetically predisposed individuals. Literature on the subject is voluminous, but the scientific impact of different studies varies widely.
Parkinson syndrome (PS) is diagnosed when two of the three—bradykinesia, rigidity, and resting tremor—are detected. Parkinson's disease, which accounts for a majority of cases,1-5 is diagnosed when Lewy body (LB) pathology is noted.6 Because the clinical diagnosis of PD may be incorrect in a large proportion,5,7 studies based on only clinical assessment include several diverse variants of PS rather than single disease entity. It is reasonable to assume that the cause for all different variants of PS is not the same.
For a critical analysis of the literature, the following well-known facts must be taken into consideration: (1) PD is ubiquitous; (2) the mean onset age is approximately 62 years, the frequency
Ali H. Rajput. Environmental Causation of Parkinson's Disease. Arch Neurol. 1993;50(6):651–652. doi:10.1001/archneur.1993.00540060081022