INTRODUCTION: Parkinson's disease (PD) is characterized by bradykinesia, 
rigidity, postural instability and tremor. Several pathologic processes can 
produce this syndrome, but neurodegeneration accompanied by neuronal inclusions 
composed of α-synuclein (Lewy bodies) is considered the typical pathologic 
correlate of PD.
METHODS: The neuropathologic features of PD are reviewed based upon personal 
experience and review of the literature. Molecular pathology of PD is summarized 
from cell biological and animal studies.
RESULTS: The pathologic feature that correlates with signs and symptoms of PD is 
neuronal loss in the substantia nigra with dopaminergic denervation of the 
striatum. Neuronal degeneration in the substantia nigra preferentially affects 
the ventrolateral cell group that projects to posterolateral putamen and is 
accompanied by formation of Lewy bodies composed of aggregated α-synuclein. Some 
patients with PD are found at autopsy to have other pathologic processes, such 
as multiple system atrophy, progressive supranuclear palsy and cerebrovascular 
disease (vascular Parkinsonism). The peripheral autonomic nervous system is also 
affected. The triggering event in PD is unknown, but recent studies suggest a 
role for loss of nuclear membrane integrity. Once α-synuclein aggregates forms, 
evidence supports cell-to-cell propagation.
CONCLUSION: PD is a multisystem synucleinopathy caused by poorly characterized 
genetic and environmental factors that produces degeneration in selectively 
vulnerable neuronal populations.