Published on: December 11, 2018
Parkinson’s disease (PD) mainly affects the body’s motor system. It’s symptoms – which result from the long-term degeneration of the central nervous system – occur over time and include shaking, difficulty walking, slow movements, and rigidity. People with PD may also experience behavioral and cognitive disturbances. This is not to suggest that everyone with PD also experiences dementia. Rather, cognitive disturbances that impact thinking are present in all individuals who have PD.
Even so, it is not yet possible to have a complete understanding of the impacted brain regions. Quite simply, most PD studies do not compare research participants to “healthy control groups” of individuals who are the same age and do not have PD. Such controls would provide researchers with a standard they could use to make comparisons and strengthen their conclusions. With respect to the topic at hand, healthy control groups are necessary to determine whether cognitive deficits in people with PD (but without dementia) are the result of disease-specific mechanisms or due to normal aging.
What we do know is that there are sex differences in the prevalence of PD – i.e., men are more likely to have the disease and women tend to have less noticeable motor symptoms. Yet, sex differences in the cognitive performances of people with PD are inconsistent and have been largely based on qualitative reports.
Gaining a more complete understanding of the cognitive profile of people with PD (without dementia) and the sex differences related to their cognitive deficits will improve our understanding of the overall cognitive mechanisms involved in Parkinson’s disease.
To this end, our research team – within the Canadian Consortium on Neurodegeneration in Aging (CCNA) – combined the results of a number of studies (i.e., conducted a meta-analysis) to compare the performance of people with PD (without dementia) relative to healthy controls across three cognitive domains: frontal executive, verbal memory, and visuospatial function. We also examined whether men and women with PD show differences in their level of deficit across these cognitive domains.
Our findings – published in Parkinsonism & Related Disorders – revealed that people with PD (without dementia) experience moderate deficits in all three cognitive domains relative to a healthy control group. Additionally, we found that there are significant sex differences in frontal executive abilities; males with PD have greater deficits than females (relative to the controls). We also examined the potential impact of disease duration, motor symptom severity, education, the presence of depression, and dosage of PD medication. None of these factors were associated with cognitive deficits in any of the categories we examined.
Our findings suggest that wide-spread cognitive impairment is an important feature of the PD profile of those who are not diagnosed with dementia. Sex-related factors (e.g., the protective effects of estrogen against the loss of dopamine) may protect women (who have PD, but not dementia) against more severe deficits in frontal executive function. Our results contribute to a growing body of literature on sex differences in PD, which could facilitate the sex-specific clinical treatment of PD.
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