Neurobiology of cognitive impairment in Parkinson's disease

Cognitive impairment is a frequent complication of Parkinson's disease (PD). Mild cognitive impairment (MCI) may progress to dementia more frequently and rapidly. PD dementia (PDD) and PD-MCI have a mean prevalence up to 75% each; a four- to six-times increased incidence rate compared with controls. Recent diagnostic clinical criteria for both PDD and PD-MCI require validation. Cognitive decline in PD can be probed clinically, comprehensive neuropsychological assessment being the best way to define it. Neuroimaging in both disorders revealed cortical atrophy, hypometabolism, white matter changes, dopaminergic/cholinergic dysfunction and increased amyloid burden. Combined analysis of imaging and cerebrospinal fluid markers (tau and Aβ-42) is the most promising method for indentifying PD-MCI and PDD. Morphological substrates are a combination of Lewy and Alzheimer pathologies causing destruction of essential neuronal networks. PDD and dementia with Lewy bodies are considered similar parts of a disease spectrum. Treatment with cholinesterase inhibitors revealed mild-to-moderate results.