Spectrum of Parkinson's disease, Parkinson's dementia, and Lewy body dementia.

Dementia occurs more commonly in individuals with Parkinson's disease (PD) than in the age-matched general population. Dementia in PD may result from a mixture of cortical and subcortical dementia syndromes caused by a variety of underlying pathologic processes and neurochemical deficits. A primary dementia syndrome has been described that shares several pathologic and clinical characteristics with PD. Dementia with Lewy bodies (DLB) accounts for 15% to 20% of all dementia syndromes in old age, which makes it second only to Alzheimer's disease in prevalence. The relationship between dementia in PD and DLB has not been fully resolved but may be considered useful in terms of neuropathologic substrate, clinical features, and response to treatment.