Comparative features of the epidemiology of multiple sclerosis and Parkinson's disease: environmental factors of potential etiological importance.

Multiple sclerosis (MS) and Parkinson's disease (PD) are diseases of unknown cause. The etiology of MS is usually considered to be due to a number of potential biological agents while the etiology of PD is usually associated with toxic agents. Despite these differences, both pathologies have strong epidemiological similarities. A comparative analysis is performed of the epidemiology of MS and PD. Potential causal factors for PD may include dopamine-like pharmacological agents. It is proposed that potential causal agents such as certain drugs plus certain vaccines could explain rationally the epidemiology of MS. Ecology and genetics could not be the appropriate lines of research in the etiology of MS/PD because they are supported only in part by the epidemiology.