Increased perivascular space volume in white matter and basal ganglia is associated with cognition in Parkinson's Disease

Concomitant Pathologies and Their Impact on Parkinson Disease: A Narrative Overview of Current Evidence

Many clinico-pathological studies point to the presence of multiple comorbidities/co-pathologies in the course of Parkinson disease (PD). Lewy body pathology, the morphological hallmark of PD, rarely exists in isolation, but is usually associated with other concomitant pathologies, in particular Alzheimer disease-related changes (ADNC), cerebrovascular pathologies (macro- and microinfarcts, cerebral small vessel disease, cerebral amyloid angiopathy), TDP-43 pathology as well as multiple pathological combinations. These include cardiovascular disorders, metabolic syndrome, diabetes mellitus, autoimmune and rheumatic diseases, myasthenia gravis, Sjögren's syndrome, restless leg syndrome or other rare disorders, like Fabry disease. A combination of PD and multiple sclerosis (MS) may be due to the immune function of LRRK2 and its interrelation with α-synuclein. COVID-19 and HIV posed considerable impacts on patients with PD. Epidemiological evidence points to a decreased risk for the majority of neoplasms, except melanoma and other skin cancers, while some tumors (breast, brain) are increased. On the other hand, a lower frequency of malignancies preceding early PD markers may argue for their protective effect on PD risk. Possible pathogenetic factors for the association between PD and cancer are discussed. The tremendous heterogeneity of concomitant pathologies and comorbidities observed across the PD spectrum is most likely caused by the complex interplay between genetic, pathogenic and other risk factors, and further research should provide increasing insight into their relationship with idiopathic PD (and other parkinsonian disorders) in order to find better diagnostic tools and probable disease-modifying therapies.

Diffusion Tensor Image Analysis ALong the Perivascular Space (DTI-ALPS): Revisiting the Meaning and Significance of the Method

More than 5 years have passed since the Diffusion Tensor Image Analysis ALong the Perivascular Space (DTI-ALPS) method was proposed with the intention of evaluating the glymphatic system. This method is handy due to its noninvasiveness, provision of a simple index in a straightforward formula, and the possibility of retrospective analysis. Therefore, the ALPS method was adopted to evaluate the glymphatic system for many disorders in many studies. The purpose of this review is to look back and discuss the ALPS method at this moment.The ALPS-index was found to be an indicator of a number of conditions related to the glymphatic system. Thus, although this was expected in the original report, the results of the ALPS method are often interpreted as uniquely corresponding to the function of the glymphatic system. However, a number of subsequent studies have pointed out the problems on the data interpretation. As they rightly point out, a higher ALPS-index indicates predominant Brownian motion of water molecules in the radial direction at the lateral ventricular body level, no more and no less. Fortunately, the term "ALPS-index" has become common and is now known as a common term by many researchers. Therefore, the ALPS-index should simply be expressed as high or low, and whether it reflects a glymphatic system is better to be discussed carefully. In other words, when a decreased ALPS-index is observed, it should be expressed as "decreased ALPS-index" and not directly as "glymphatic dysfunction". Recently, various methods have been proposed to evaluate the glymphatic system. It has become clear that these methods also do not seem to reflect the entirety of the extremely complex glymphatic system. This means that it would be desirable to use various methods in combination to evaluate the glymphatic system in a comprehensive manner.

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.