Cognitive impairment and dementia in patients with Parkinson disease.

Parkinson disease (PD) is an already prevalent neurodegenerative disease that is poised to at least double over the next 25 years. Although best known for its characteristic movement disorder, PD is now appreciated commonly to cause cognitive impairment, including dementia, and behavioral changes. Dementia in patients with PD is consequential and has been associated with reduced quality of life, shortened survival, and increased caregiver distress. Here we review clinical presentation and progression, pathological bases, identification of genetic risk factors, development of small molecule biomarkers, and emerging treatments for cognitive impairment in patients with PD.