Cognitive dysfunction (primarily executive, visuospatial and memory function) can occur in Parkinson disease as a result of cortical and subcortical changes, with an estimated 20-40% of patients eventually developing dementia (Bosboom et al. J Neural Transm 2004;111:1303-1315).  The pathophysiology of PD dementia has not been fully elucidated but may be due, in part, to cholinergic deficiency in the cerebral cortex, cortical Lewy bodies and other Alzheimer disease-like pathology.