Dementia affects about 40% of patients with
Parkinson's disease; the incidence of
dementia in these patients is up to six times that in healthy people. Clinically, the prototype of
dementia in PD is a dysexecutive syndrome. Loss of
cholinergic, dopaminergic, and noradrenergic innervation has been suggested to be the underlying neurochemical deficits. Nigral pathology alone is probably not sufficient for the development of
dementia. Although there is some controversy with regard to the site and type of pathology involved,
dementia is likely to be associated with the spread of pathology to other subcortical nuclei, the limbic system, and the cerebral cortex. On the basis of more recent studies, the main pathology seems to be Lewy-body-type degeneration with associated cellular and synaptic loss in cortical and limbic structures.
Alzheimer's disease-type pathology is commonly associated with
dementia but less predictive. Recent evidence from small studies suggests that
cholinesterase inhibitors may be effective in the treatment of
dementia associated with PD.