Study: Dementia diagnosed later in Parkinson’s disease course

Key takeaways:

• Among people with Parkinson’s disease, dementia tends to be diagnosed later in the course of PD.
• The estimated risk for dementia rose as high as 90% after 25 years of PD diagnosis and beyond.

In two large trials of individuals with Parkinson’s disease, dementia occurred less frequently and later in the disease course than previously thought, according to new research published in Neurology.

“Treatment of PD cognitive impairment lags treatment of motor symptoms,” Julia Gallagher, BS, research coordinator at the Parkinson’s Disease and Movement Disorders Center in the neurology department at the Perelman School of Medicine at the University of Pennsylvania, and colleagues wrote. “To optimize clinical management, better understand progression to dementia and spur treatment development, accurate estimates of long-term dementia rates are needed.”

Decades-old data cite that dementia occurs in up to 80% of patients with PD, Gallagher and colleagues wrote. So, they sought to bring research up to date by determining long-term dementia risk in PD among participants of two large, ongoing, prospective, observational studies: the Parkinson’s Progression Markers Initiative (PPMI), a multisite international study, as well as a longstanding PD research cohort study at the University of Pennsylvania.

The PPMI cohort was comprised of 417 participants with PD (mean age 61.6 years; 65% male) who underwent an annual cognitive battery. Cognitive diagnoses were made by the site investigators.

The Penn cohort was comprised of 389 participants with PD (mean age 69.3 years; 67% male) who submitted to a comprehensive cognitive battery every year for the first 4 years then every other year thereafter, with cognitive diagnosis made via expert consensus.

The researchers analyzed the time from PD diagnosis to stable dementia diagnosis for each cohort. The primary endpoint was cognitive diagnosis of dementia. Secondary endpoints were scores of less than 21 on the Montreal Cognitive Assessment (MoCA) and three or higher on the Movement Disorder Society—Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) Part I.

No participants in the PPMI cohort were diagnosed with dementia at baseline, but 28 (7%) were diagnosed by year 10 and 34 (8.5%) were diagnosed over the entire follow up. The estimated probability of developing dementia by year 10 of PD diagnosis was 9% for site investigator diagnosis, 15% based on the MoCA cutoff or 12% based on the MDS-UPDRS Part I cognition score.

For the Penn cohort, 42 (10.8%) were diagnosed with dementia at baseline and 184 (47.3%) received a diagnosis at some interval during the evaluation process. In a statistical analysis undertaken by the researchers, the interval-censored curve for the Penn cohort had a median time to dementia of 15 years (95% CI, 13–15), while the estimated probability of dementia was 27% at 10 years, 50% at 15 years and 74% at 20 years.

Data further showed that, when combining both cohorts, the estimated risk for dementia by PD duration was 3% to 12% at year 5, 9% to 27% at year 10, 50% at year 15, 74% at year 20 and 90% from year 25 and beyond.

“These results provide updated and more hopeful estimates of long-term dementia risk in PD, suggesting a longer window to intervene to prevent or delay cognitive decline,” Gallagher and colleagues wrote.