Is the cingulate island sign a marker for early dementia conversion in Parkinson's disease?

Risk of Dementia in Parkinson's Disease: A Systematic Review and Meta-Analysis

Estimates of the risk of dementia in Parkinson's disease (PDD) vary widely. We aimed to review the incidence of PDD and in a meta-analysis estimate the pooled annual incidence and relative risk of PDD while also exploring factors that may contribute to heterogeneity between studies. Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines were followed and MEDLINE and EMBASE were searched for articles reporting the number of cases of dementia in a population, followed longitudinally, with a minimum of 100 dementia-free Parkinson's disease (PD) patients at baseline. Meta-analyses and meta-regressions were used to estimate the pooled incidence rate of PDD and the relative risk of PDD versus healthy controls (HC). A total of 32 studies were identified, 25 reporting the incidence of PDD and 10 reporting the relative risk of PDD versus HC. The pooled incidence rate of PDD was 4.45 (95% confidence interval [CI], 3.91-4.99) per 100 person-years at risk, equating to a 4.5% annual risk of dementia in a PD prevalent population. The relative risk of PDD was estimated to be 3.25 (95% CI, 2.62-4.03) times greater than HC. Factors contributing to study heterogeneity and disparities in the estimated risk of PDD include the age of patients, year of recruitment, and study location. Significant gaps remain with no studies identified in several geographical regions. Future studies should stratify by age and standardize reporting to reduce overall heterogeneity. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Pathobiology of Cognitive Impairment in Parkinson Disease: Challenges and Outlooks

Cognitive impairment (CI) is a characteristic non-motor feature of Parkinson disease (PD) that poses a severe burden on the patients and caregivers, yet relatively little is known about its pathobiology. Cognitive deficits are evident throughout the course of PD, with around 25% of subtle cognitive decline and mild CI (MCI) at the time of diagnosis and up to 83% of patients developing dementia after 20 years. The heterogeneity of cognitive phenotypes suggests that a common neuropathological process, characterized by progressive degeneration of the dopaminergic striatonigral system and of many other neuronal systems, results not only in structural deficits but also extensive changes of functional neuronal network activities and neurotransmitter dysfunctions. Modern neuroimaging studies revealed multilocular cortical and subcortical atrophies and alterations in intrinsic neuronal connectivities. The decreased functional connectivity (FC) of the default mode network (DMN) in the bilateral prefrontal cortex is affected already before the development of clinical CI and in the absence of structural changes. Longitudinal cognitive decline is associated with frontostriatal and limbic affections, white matter microlesions and changes between multiple functional neuronal networks, including thalamo-insular, frontoparietal and attention networks, the cholinergic forebrain and the noradrenergic system. Superimposed Alzheimer-related (and other concomitant) pathologies due to interactions between α-synuclein, tau-protein and β-amyloid contribute to dementia pathogenesis in both PD and dementia with Lewy bodies (DLB). To further elucidate the interaction of the pathomechanisms responsible for CI in PD, well-designed longitudinal clinico-pathological studies are warranted that are supported by fluid and sophisticated imaging biomarkers as a basis for better early diagnosis and future disease-modifying therapies.