[The neuropathology of Parkinson syndrome]

Parkinsonism is due to an alteration of the dopaminergic nigro-striatal pathway the main morphological basis of which is a lesion of the substantia nigra (SN). Parkinson's disease, the etiology of which is unknown, is responsible for 90 p. cent of the cases of parkinsonism. It is characterized by a neuronal loss involving mainly the pigmented brainstem nuclei (substantia nigra, locus coeruleus and dorsal vagal nuclei) and a specific neuronal inclusion: the Lewy inclusion body. Involvement of other structures such as the nucleus basalis of Meynert, hypothalamus, reticular formations of the brainstem, spinal lateral horns, sympathetic ganglia, may be responsible for dementia and/or autonomic failure which are often associated with the extrapyramidal signs. Various other pathological processes, infectious, toxic, vascular, tumoral or traumatic, involving usually the SN, are occasionally responsible for parkinsonism. A number of degenerative diseases involving the SN may develop parkinsonism as major presenting sign. Most of them are diseases of the basal ganglia such as multiple system atrophy, primitive pallidal atrophies, Steele-Richardson-Olszewski disease, Hallervorden-Spatz disease. However, changes in the SN at the origin of parkinsonism are occasionally found in cortical degenerative diseases such as senile dementia of Alzheimer's type, Pick disease or the complex of Guam, in cerebellar atrophies or in motor neuron disease.