Neuropsychological characteristics of dementia with Lewy bodies and Parkinson's disease with dementia: differentiation, early detection, and implications for "mild cognitive impairment" and biomarkers.

Parkinson's disease with dementia (PDD) and dementia with Lewy bodies (DLB) are neurodegenerative conditions sharing a disorder of alpha-synuclein metabolism. Temporal differences in the emergence of symptoms and clinical features warrant the continued clinical distinction between DLB and PDD. While DLB and PDD groups' neuropsychological profiles often differ from those in Alzheimer's disease (AD), the diagnostic sensitivity, specificity, and predictive values of these profiles remain largely unknown. PDD and DLB neuropsychological profiles share sufficient similarity to resist accurate and reliable differentiation. Although heterogeneous cognitive changes (predominantly in memory and executive function) may manifest earlier and more frequently than previously appreciated in Parkinson's disease (PD), and executive deficits may be harbingers of dementia, the enthusiasm to uncritically extend the concept of mild cognitive impairment (MCI) to PD should be tempered. Instead, future research might strive to identify the precise neuropsychological characteristics of the prodromal stages of PD, PDD, and DLB which, in conjunction with other potential biomarkers, facilitate early and accurate diagnosis, and the definition of neuroprotective, neurorestorative, and symptomatic treatment endpoints.