[Dementia and cognitive impairment in Parkinson disease]

Changes in cognitive function and disturbances in behavior are commonly seen in parkinsonian patients and they are inherent features of the disease. Estimates on the prevalence of dementia in this disorder are quite variable, ranging from 15 to 25%. Advanced age, depression, severity of akinesia, and the presence of dopaminomimetic psychosis, are considered as risk factors in the development of cognitive deterioration within this patient population. Cognitive dysfunction may manifest as relatively circumscribed deficits or overt dementia. The finding of mild cognitive deficits is common in Parkinson's disease, such as reduced flexibility, psychomotor slowing, reduction in learning capacity and information retrieval, and disturbances in visuospatial tasks. The most prevalent cognitive disturbance is an impairment in visuospatial tasks, not necessarily related to the degree of motor disability. Dementia, when present early on in the course of the disease may suggest alternative diagnoses (Diffuse Lewy body dementia, Alzheimer's disease with extrapyramidal features, Fronto-temporal dementia, etc.), while in those cases in whom the dementing disorder develops at a later stage, it is assumed to be an integral part of the disease, albeit corresponding to variable pathogenetic mechanisms.