Let's not forget about cognition..

There have been a few recent studies looking at cognition before development of Parkinson's Disease and this nice review paper from Germany brings a lot of the important findings together. There is a building consensus that a sub-clinical decline in cognition (i.e. problems with memory and thinking that are not severe enough to impair daily living) is present in a number of patients before development of Parkinsons Disease. However, it is also clear that not all patients have these problems - I think, as with Parkinsons subtypes, teasing out the differences between these patients may well shed further light on the underlying disease process.

Conceptually, there are different ways of looking at the time before Parkinson's diagnosis - probably the most robust being large prospective population studies which have been able to look at participants over many years until a proportion develop Parkinsons. Only 4 of these were identified and it is difficult to compare them directly due to differing methodologies; 2 of these studies showed poorer cognitive performance in those who eventually developed Parkinsons, 1 didn't show a difference and the final study didn't directly compare this outcome. 

Another methodology, the one used in PREDICT-PD, is identifying participants at higher risk of Parkinsons disease to see whether there are differences in cognition between higher and lower risk groups. The PARS study looked at participants with two risk markers - poor smell and reduced dopamine binding on PET scan and found significant differences in 2 aspects of cognition. In PREDICT-PD, we have also found poorer overall cognitive scores in the higher risk group. 

The authors are circumspect about the limitations of the studies so far and certainly there are a number of studies, particularly in popluations with genetic risk for Parkinsons disease, which don't show positive findings. However, by combining findings in specific domains, there are definite signs that poorer executive function is commonly found before diagnosis of Parkinsons. 

Presence of Cognitive Impairment in prodromal Parkinsons Disease by study type, from Fengler et al, Cognitive Changes in prodromal Parkinson's disease: A review. 

We continue to work on cognition in our cohort - for the moment it's a case of watch this space. 

-Anna


https://www.ncbi.nlm.nih.gov/pubmed/28980730

Mov Disord. 2017 Oct 5. doi: 10.1002/mds.27135. 

Cognitive changes in prodromal Parkinson's disease: A review. 

Fengler S, Liepelt-Scarfone I, Brockmann K, Schäffer E, Berg D, Kalbe E 

Although other nonmotor phenomena representing possible prodromal symptoms of Parkinson's disease have been described in some detail, the occurrence and characteristics of cognitive decline in this early phase of the disease are less well understood. The aim of this review is to summarize the current state of research on cognitive changes in prodromal PD. Only a small number of longitudinal studies have been conducted that examined cognitive function in individuals with a subsequent PD diagnosis. However, when we consider data from at-risk groups, the evidence suggests that cognitive decline may occur in a substantial number of individuals who have the potential for developing PD. In terms of specific cognitive domains, executive function in particular and, less frequently, memory scores are reduced. Prospective longitudinal studies are thus needed to clarify whether cognitive, and specifically executive, decline might be added to the prodromal nonmotor symptom complex that may precede motor manifestations of PD by years and may help to update the risk scores used for early identification of PD. © 2017 International Parkinson and Movement Disorder Society.