Do people with Parkinson’s always develop dementia?

• Dementia for people with Parkinson’s disease may occur less often, and when it does occur, may develop later, a new study suggests.
• Two new investigations have found that early understanding of dementia’s inevitability for Parkinson’s patients has been significantly overstated.
• One of the new investigations found that less than 10% of people with the disease had developed dementia 10 years after diagnosis.

For people with Parkinson’s disease, dementia develops less frequently and takes longer to develop than was previously believed, according to a new study analyzing two investigations of dementia and Parkinson’s.

It has been believed that dementia occurred in about 80% of people who had Parkinson’s as early as eight years after diagnosis . In one of the investigations, just 9% of people with Parkinson’s had dementia at 10 years, and the second reported a 27% incidence at that time.

The first investigation noted above was conducted by the Parkinson’s Progression Markers Initiative (PPMI), which is a public-private partnership, in part funded by the Michael J. Fox Foundation for Parkinson’s Research. The second investigation comes from the University of Pennsylvania study and was supported by the National Institute on Aging.

The PPMI investigation collected data from 417 people with Parkinson’s as well as from healthy controls from 24 study sites in the U.S., Europe, and Australia. Each participant was required to have received their diagnosis within the last two years, be 30 years of age or older, and be untreated. They were assessed cognitively at yearly visits. Their average age at the end of the study was 62.

The University of Pennsylvania investigation involved 389 people with Parkinson’s, with an eventual average age of 69, who had been diagnosed with Parkinson’s six years before the start of the study. They were visited and cognitively assessed annually for the first four years of participation, and then biennially until the end of the study.

The PPMI study found that no participants had dementia at the start of their investigation, compared to the University of Pennsylvania research, which found a 10.8% incidence of dementia at that time. This may be explained by the two-year diagnosis window used in the former investigation versus the six-year window of the latter.

Of the participants, 8.5% were diagnosed with dementia over the entire follow-up period. The highest overall percentage of people with Parkinson’s developing dementia was 11.8% when the researchers used an alternate definition for dementia as defined by the Montreal Cognitive Assessment (MoCA), a test to detect mild cognitive impairment.

The University of Pennsylvania results tell a bit different story. Ultimately, they draw close to the traditional 80% dementia estimate for people with Parkinson’s, if more slowly. This report found a 50% chance of dementia 15 years after diagnosis, with a 74% chance at 20 years.

The study is published in Neurology .

Cognitive decline in Parkinson’s may vary

The notion that dementia associated with Parkinson’s may develop more slowly and less often may mean an extension of cognitive quality of life than was previously assumed.

“The results from the Penn cohort suggest that dementia occurs later in the disease course than previously thought. The results are even more striking for the PPMI cohort,” said the study’s senior investigator Daniel Weintraub, MD , professor of psychiatry at the Hospital of the University of Pennsylvania in Philadelphia.

Daniel Truong, MD , neurologist and the medical director of the Truong Neuroscience Institute at MemorialCare Orange Coast Medical Center in Fountain Valley, CA, who was not involved in the study, told Medical News Today , “The findings from this study do resonate with some clinical experiences and emerging research trends.”

“Recent observations indicate that cognitive decline might progress more slowly,” said Truong, “especially in patients diagnosed at a younger age or those with higher educational backgrounds.”

“This study aligns with a growing recognition that Parkinson’s cognitive outcomes can be quite variable, underscoring the importance of personalized patient management,” Truong said.

Dementia caused by other factors

“The longer-term dementia risk observed in this study, particularly in older patients,” noted Truong, “could be influenced by several factors beyond Parkinson’s itself.”

“Age-related cognitive decline, Alzheimer’s disease, and other neurodegenerative or vascular conditions become more prevalent as people age, complicating the ability to definitively attribute cognitive decline solely to Parkinson’s,” he cautioned.

Weintraub was encouraged that, “The age of the Parkinson’s participants in our cohorts is similar to that in other studies, and the age at disease onset for the PPMI participants was similar to that reported for Parkinson’s on average (low 60s).”

Even so, he added, “No study, including ours, can say definitely what might be the cause of dementia in a given participant. That can only be examined on autopsy.”

“In general, the etiology of dementia in Parkinson’s is thought to be a mix of Lewy body pathology primarily, but, also to varying extents, Alzheimer’s disease pathology and vascular disease,” explained Weintraub.

“The complex interplay between Parkinson’s and age-related conditions suggests that in older patients, the cognitive decline might be multifactorial, rather than solely due to Parkinson’s. The role of other age-related factors cannot be ignored, especially in older cohorts. Further research that isolates the contributions of Parkinson’s from other age-related factors would help clarify this relationship.”
— Daniel Truong, MD

A change in Parkinson’s care?

“The findings of less frequent and later-onset dementia in Parkinson’s disease could impact how care for Parkinson’s patients is structured and delivered,” Truong proposed.

“Cognitive monitoring may be adjusted to focus more on long-term evaluation rather than assuming rapid decline,” he said.

“People with Parkinson’s might indeed suffer from unfair expectations that cognitive decline is imminent, leading to unnecessary anxiety or stigma,” Truong said.

“Hopefully, it will be reassuring for patients to hear that dementia is not ‘inevitable’ in Parkinson’s disease and that it may be common to live with the illness for many years without developing significant cognitive impairment.”
— Daniel Weintraub, MD

“The study emphasizes the need for more nuanced and individualized projections about the progression of cognitive symptoms in Parkinson’s. A more balanced approach to Parkinson’s care may be needed. It should focus on individual patient needs rather than a one-size-fits-all assumption of inevitable cognitive decline,” concluded Truong.