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Cognitive Decline in Parkinson's Disease

There are many studies on cognitive and behavioral alterations in Parkinson’s disease, but each of these investigations brought only a small piece of a large puzzle. Consequently, our knowledge of the mental alterations in Parkinson’s disease, and their impact on functional status and well-being, may be incomplete or distorted.

Project Description:
Between 2002 and 2005, we extensively examined 120 newly diagnosed patients with Parkinson’s disease and 70 healthy elderly with neuropsychological tests covering six domains of cognitive functioning: psychomotor speed, attention, language, memory, executive functions, and visuospatial skills. Physical symptoms, functioning in daily life, and quality of life were assessed by a neurologist, using standardized rating scales. After three years, patients and controls were evaluated again. We will now assess the participants for the third time with the same tests and rating scales. We expect that at least 80 patients and 55 of the healthy elderly will continue to participate. The degree and pattern of cognitive decline will be analyzed, and we will attempt to identify the characteristics that predict cognitive decline.

Relevance to Diagnosis/Treatment of Parkinson’s Disease:
The results of this study will allow us to describe the profile of cognitive and behavioral changes in more detail, and hopefully we will discover the characteristics that are predictive for functional and mental decline after five years. We expect that our study will contribute to a better understanding of the clinical presentation of Parkinson’s disease and to better patient management, especially in the early stages of the disease.

Anticipated Outcome:
We expect to find that most -- if not all -- cognitive domains decline, and that this decline is not merely due to impaired executive functioning, as is generally believed.

More precise information on the profile of cognitive changes may influence the way neuroscientists think of Parkinson’s disease, e.g. no longer as mainly a disease of the basal ganglia, but also of the cerebral cortex.

Progress Report

Sixty patients and 40 control subjects participated in the 5-years follow-up. Forty-two percent of the patients were cognitively impaired to some extent (versus 3% of control subjects). These impairments concerned most often executive functioning, i.e. abstract reasoning, problem solving, and planning one’s own behavior, but also psychomotor slowness, and visuospatial problems.

Cognitive functioning had declined more than what one may expect on the basis of normal aging in 64% of the patients. Looking back to the first assessment soon after the diagnosis, it appears that this decline in cognitive functioning over five years is best predicted by the early presence of axial motor symptoms and forgetfulness. Axial symptoms are, for example, problems with walking and keeping balance.

Our results corroborate the prevailing idea that executive dysfunctions cause impairments in other cognitive domains.

We lost more participants during the follow-up interval than we had hoped for. This was mainly due to severe illness and death in the patient group, and to loss of motivation in the control group. The patients who dropped out of the study were older and more severely ill than the patients who continued. Thus, the percentages of decline and impairment in the patient group are probably even higher than the numbers mentioned here.

Presentations & Publications


Broeders, M., Muslimovic, D., de Bie, R., Speelman, J.D., & Schmand, B. Cognitive decline in Parkinson’s disease – A 5-year follow-up study.

10th international conference on Alzheimer and Parkinson’s diseases, Barcelona, Spain (2011, May).

Broeders, M., Muslimovic, D., Velseboer, D.C., de Bie, R., Speelman, J.D., de Vries, S., & Schmand, B. Mild cognitive impairment in newly-diagnosed PD – A 5-year longitudinal study.

8th international congress on mental dysfunction and other non-motor features in Parkinson’s disease and related disorders, Berlin, Germany (2012, May).


Broeders, M., Velseboer, D.C., de Bie, R., Speelman, J.D., Muslimovic, D., Post, B., de Haan, R., & Schmand, B. (2012) Cognitive change in newly-diagnosed patients with Parkinson disease – A 5-year follow-up study. Manuscript submitted for publication.

Broeders, M., de Bie, R., Velseboer, D.C., Speelman, J.D., Muslimovic, D., & Schmand, B. (2012) The evolution of mild cognitive impairment in Parkinson disease. Manuscript submitted for publication.

Velseboer, D.C., Broeders, M., Post, B., van Geloven, H., Speelman, J.D., Schmand, B., de Haan, R., & de Bie, R. (2012) Prognostic factors of impairment, disability and quality of life in newly diagnosed Parkinson’s disease. Manuscript submitted for publication.

November 2012


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