Evolution of concepts and definitions of Parkinson's disease since 1817.

In the first half of the nineteenth century many patients suffering from multiple sclerosis, amyotrophic lateral sclerosis, tabes dorsalis, neuropathy and myopathy were in general described as a paralysis, paralysis agitans, and used 'lessened muscular power' to characterize the disorder. In this article we will review various definitions of Parkinson's disease, which appeared in textbooks since the original description and demonstrate that the number of symptoms as well as the selection of the symptoms in those definitions varied, although the different definitions clearly referred to the same disease.