Dementia in Parkinson Disease Occurs Less Often, Develops Slower

Dementia in Parkinson disease (PD) is less frequent and occurs later in the disease course than previous research has suggested, according to an analysis of 2 studies published in Neurology.

A frequently reported statistic is that Parkinson disease dementia (PDD) occurs among at least 80% of patients. However, conflicting data about the incidence of PDD have been published.

To clarify the long-term risk for PDD, researchers from the Parkinson’s Progression Markers Initiative (PPMI) sourced data for this study from 2 large, prospective, observational studies, the PPMI, an international, long-standing PD research cohort and a single-center cohort study from the University of Pennsylvania (Penn).

The primary endpoint in this study was the time from PD diagnosis to stable dementia.

The PPMI (n=417; men, 65%; mean age, 61.6; age 56-70 at PD diagnosis, 51%; White, 92%) and Penn (n=389; men, 67%; mean age, 63.3; age 56-70 at PD diagnosis, 55%; White, 93%) cohorts had a mean Movement Disorder Society—Unified Parkinson’s Disease Rating Scale part III (MDS-UPDRS III) score of 20.9 and 28.2, and median Montreal Cognitive Assessment (MoCA) score of 28 and 26, respectively.

With a baseline PD duration of between 0-3 years (mean, 0.6 years) and during a 10-year follow-up, the overall rate of dementia in the PPMI cohort was 8.5%. Using alternative definitions of dementia, the rate of dementia in the PPMI cohort was 9.8% using MoCA and 7.4% using MDS-UPDRS I scores. The median time to dementia could not be estimated.

For Penn, the patients had a PD duration of between 0-32 years (mean, 6.3 years) at baseline and attended an average of 4.6 follow-up visits at 1-to-2-year intervals. During that time, the rate of dementia was 47.3%, in which the median time to dementia from PD diagnosis was 15.2 (95% CI, 13.3-15.2) years.

Stratified by age at diagnosis, the median time to dementia was 19.4 years for those diagnosed before age 56, 14.6 years for those diagnosed at ages 56-70, and 9.2 years for those diagnosed older than age 70 (P <.001).

Stratified by gender, men had a significantly shorter time to dementia after diagnosis than women (median, 13.3 vs 19.4 years; P =.004), respectively.

Time to dementia also depended on educational attainment, in which dementia occurred sooner after diagnosis for those who completed 13 years or less of education compared with those attending more than 13 years (median, 11.6 vs 15.2 years; P =.006), respectively.

This study was limited by missing data, in which 36.2% of the PPMI and 13.6% of the Penn cohorts either withdrew consent or were lost to follow-up.

“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,” the researchers concluded.

Disclosure: This research was supported by Michael J Fox Foundation for Parkinson’s Research and funding partners. Please see the original reference for a full list of disclosures.