Hidden Alzheimer’s warning signs found in Parkinson’s patients without dementia

In this study, led by first author Keiko Hatano and corresponding author Masashi Kameyama from the Tokyo Metropolitan Institute for Geriatrics and Gerontology in Japan, researchers found that patients with Parkinson's disease (PD) diagnosed in their 80s showed a significantly higher rate of amyloid positivity -- an indicator associated with Alzheimer's disease -- compared to those diagnosed at a younger age. Importantly, none of the participants had dementia. These findings suggest that older patients with PD may face a greater risk of future cognitive decline and could benefit from early screening for Alzheimer's-related brain changes.

Amyloid-beta is considered a key marker of cognitive decline. While it is known that amyloid accumulation contributes to PD with dementia, its role in patients who have not developed cognitive problems remains less understood. This study aimed to explore how age influences amyloid buildup in people with PD who do not yet show signs of dementia.

The researchers analyzed data from 89 individuals with PD and no signs of dementia. Participants were divided into two age-based groups: those diagnosed before age 73 (LOW group) and those diagnosed at age 73 or older (HIGH group). Using cerebrospinal fluid samples, they measured levels of amyloid-beta, a standard method for detecting early Alzheimer's-related changes. The findings revealed that 30.6% of the older group tested positive for amyloid, compared to just 10.0% in the younger group.

"[…] we elucidated the prevalence of amyloid positivity in patients with PD without dementia, whose mean age at diagnosis was 80.2 years, using CSF Aβ42 levels."

Interestingly, both age groups of Parkinson's patients had a lower rate of amyloid positivity than cognitively normal individuals of the same age in the general population. This unexpected result suggests that PD may alter how amyloid accumulates in the brain, possibly shortening the phase in which amyloid builds up silently before symptoms appear. The authors suggest that amyloid buildup could accelerate the transition from healthy cognition to dementia in patients with PD. The study also observed age-related associations with other biological markers of Alzheimer's disease, such as tau protein levels.

As the global population continues to age and the number of older adults diagnosed with PD grows, identifying early warning signs of cognitive decline becomes increasingly important. These findings may help inform future screening approaches and support the development of therapies aimed at delaying or preventing dementia in people with Parkinson's disease.