The morphological basis of dementia in Parkinson's disease.

The literature pertinent to the pathological anatomy subserving dementia in Parkinsonian patients is reviewed. Mechanisms discussed include cerebral cortical atrophy; hydrocephalus; Lewy body inclusions; neocortical lesions of the Alzheimer type; depletion of cholinergic, dopaminergic or noradrenergic transmitter systems; 'subcortical' dementia; and neuronal depopulation of the basal forebrain. New autopsy data are presented to confirm that, contrary to published reports, most patients with parkinsonism who exhibit dementia do not have concomitant Alzheimer's disease, and that some different pathogenetic mechanism must be sought to account for this increasingly common cause of cognitive decline in the sufferers of Parkinson's disease.