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How Common is Cognitive Decline in Parkinson's?

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A new study finds that cognitive impairment is a frequent and rapidly progressing symptom of Parkinson’s disease (PD). About half of the participants who had PD for an average of five years and had normal cognition at the beginning of the study developed mild cognitive impairment (MCI) within six years – about 11 years after PD diagnosis. Those few who developed MCI progressed to dementia within five more years. The results appear in the September 11 online edition of Neurology.

With a diagnosis of PD, most people and their physicians focus on treating and coping with movement symptoms. Yet even early in the course of disease, people with PD may have difficulty multitasking, or feel that their thinking abilities are “just not the same.”

To better understand the rate at which cognitive impairment develops, and identify risk factors for the development of cognitive impairment, researchers led by Daniel Weintraub, M.D., recruited 141 people with PD to participate in the study. All were receiving treatment at the University of Pennsylvania’s Udall Center for Parkinson’s Disease Research. On average they were 69 years old and had been living with PD for five years; 63 percent were men. All participants had normal cognition based on a battery of standard tests for people with PD. The researchers re-evaluated study participants’ cognition each year for up to six years.


  • With each year of follow-up, a greater percentage of participants had progressed to MCI, reaching 47.4 percent after six years.
  • Every participant who was diagnosed with MCI during the study, progressed to dementia within five years.
  • Men were at an increased risk of cognitive impairment as were those who had higher scores on rating scales of PD motor symptoms (higher Hoehn and Yahr and UPDRS scores), a longer time living with PD and depression.

What Does It Mean?

Many people live with PD for decades with good cognitive abilities. However, this study adds to a growing body of literature that identifies cognitive impairment as a common non-motor symptom of PD. This study is also among the first to enroll a group of participants with normal cognition and to follow the progression of their cognitive difficulties over time. Compared to other studies, this one found a more rapid rate of cognitive decline among participants.

A better understanding of how PD affects cognition can help people with PD in several ways. With testing for these difficulties early in the course of disease, more people could potentially benefit from rivastigmine (Exelon®) – the only medication approved for dementia in PD.

In addition, the study results underscore the need for better therapies to slow or stop MCI, and PD progression more generally. Most PD clinical trials focus on the motor symptoms, and this study (and others) highlight the urgent need for studies focusing on interventions to slow down the rate of cognitive changes in PD. Additionally, evaluating cognition early in the course of PD could give people the opportunity to participate in clinicaltrials. Increased awareness of MCI also can help guide people in making better informed decisions about their future care.

Experts caution that PD symptoms such as depression and apathy can affect a person’s memory and ability to focus their thinking; it is important to treat these symptoms before evaluating cognition.

A shortcoming of the study is that the participants were all so similar — nearly all were Caucasian, with a high education level (16 years on average) and in a narrow age range (62-73 years). For this reason, the results may not reflect the reality in the larger population of people with PD, in which studies suggest that age is the biggest risk factor for dementia. Studies with larger numbers of participants are needed to confirm the results. One such study, which is following 8,000 people with PD at 20 different centers, already is under way.

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