Amyloid deposition in Parkinson's disease and cognitive impairment: a systematic review

Varying degrees of cortical amyloid deposition are reported in the setting of Parkinsonism with cognitive impairment. We performed a systematic review to estimate the prevalence of Alzheimer disease (AD) range cortical amyloid deposition among patients with Parkinson's disease with dementia (PDD), Parkinson's disease with mild cognitive impairment (PD-MCI) and dementia with Lewy bodies (DLB). We included amyloid positron emission tomography (PET) imaging studies using Pittsburgh Compound B (PiB).

We searched the databases Ovid MEDLINE, PubMed, Embase, Scopus, and Web of Science for articles pertaining to amyloid imaging in Parkinsonism and impaired cognition. We identified 11 articles using PiB imaging to quantify cortical amyloid. We used the metan module in Stata, version 11.0, to calculate point prevalence estimates of patients with "PiB-positive" studies, that is, patients showing AD range cortical Aβ-amyloid deposition. Heterogeneity was assessed. A scatterplot was used to assess publication bias.

Overall pooled prevalence of "PiB-positive" studies across all three entities along the spectrum of Parkinson's disease and impaired cognition (specifically PDD, PD-MCI, and DLB) was 0.41 (95% confidence interval [CI], 0.24-0.57). Prevalence of "PiB-positive" studies was 0.68 (95% CI, 0.55-0.82) in the DLB group, 0.34 (95% CI, 0.13-0.56) in the PDD group, and 0.05 (95% CI, -0.07-0.17) in the PD-MCI group.

Substantial variability occurs in the prevalence of "PiB-positive" studies in subjects with Parkinsonism and cognitive impairment. Higher prevalence of PiB-positive studies was encountered among subjects with DLB as opposed to subjects with PDD. The PD-MCI subjects showed overall lower prevalence of PiB-positive studies than reported findings in non-PD-related MCI. © 2015 International Parkinson and Movement Disorder Society.