Mild Cognitive Decline in PD Linked to Cortical Thinning

Kate Johnson

October 07, 2013

MONTREAL, Quebec, Canada — Patients with Parkinson's disease (PD) who have mild cognitive impairment (MCI) experience faster gray-matter degradation than those with normal cognition, a finding that may signal faster progression toward dementia, researchers reported at the World Parkinson Congress (WPC) here.

"Our study possibly allows for developing methods that will allow for the early prediction of dementia in PD so that as therapies evolve we will be able to identify earlier those patients in whom we need to focus on slowing down cognitive decline," senior investigator Oury Monchi, PhD, Director of the Quebec Parkinson Network, associate director for clinical research at the Institut Universitaire de gériatrie de Montréal, and associate professor in the Department of Radiology at the University of Montréal told Medscape Medical News.

The findings "contribute an additional important dimension to the cognitive biomarker research in PD and suggest that cortical atrophy can be developed into a powerful imaging biomarker for cognitive decline in PD. A major strength of this study is its longitudinal design," commented Liana Apostolova, MD, an associate professor-in-residence of neurology at the University of California, Los Angeles, who was not involved with the study.

Dr. Monchi's group has just published a cross-sectional study showing increased cortical degradation in PD with MCI compared with PD without MCI (Mov Disord. 2013;28:1360-1369), but this new longitudinal study "shows for the first time that MCI in Parkinson's disease indeed is linked with a faster rate of gray-matter degradation, both cortical and subcortical," reported Alexandru Hanganu, MD, PhD, who presented the findings.

In addition, he added, "a positive correlation between the rate of degradation and Montreal Cognitive Assessment scores showed longitudinally that the more cognitive performance decreases, the more cortical thickness decreases over time."

The study included 32 patients who had PD with MCI (n = 17) and without MCI (n = 15), as well as 18 healthy controls.

Neuropsychological evaluation and MRI were performed at baseline and again 20 months later.

Results showed that patients with PD and MCI had a statistically significant decrease in whole brain cortical thickness (decrease of 1.34%) compared with patients with PD who did not have MCI (decrease of 0.67%) and healthy controls (decrease of 0.34%), specifically in the medial occipital cortex, the temporal lobe, and the supplementary motor area (SMA).

Subcortical images showed decreased brain volume in all groups, but patients with PD and MCI had a statistically significant decrease of volume in the amygdala and nucleus accumbens (decreases of 6.05% and 5.98%) compared with patients with PD who did not have MCI (increase of 0.58% and decrease of 0.91%) and healthy controls (increases of 0.8% and 2.19%).

Montreal Cognitive Assessment scores showed longitudinally that certain regions of thinning, namely the temporal lobe bilaterally and the central gyrus, correlated with cognitive decline.

"Considering these results along with previous data it is possible that the SMA, medial occipital lobe, and temporal lobe might be markers for predicting cognitive decline in PD," said Dr. Hanganu. "Understanding MCI from this point of view is important because those patients who might benefit from early interventions could be found and helped."

"Unfortunately, not that much can be done to slow down cognitive decline, though different labs are trying treatments that do not necessarily involve medication," added Dr. Monchi. "Having said that, cognition and nonmotor deficits are to be taken into account when a clinician decides the specific treatment for the motor symptoms."

The findings are line with recent findings from Dr. Apostolova's group in patients with PD who have established dementia (J Parkinsons Dis. 2013;3:69-76).

"Both their group and ours reported changes in the supplementary motor, premotor, inferior temporal, and lateral parietal cortices," said Dr. Apostolova. "Not surprisingly, as these areas are commonly associated with executive function and visuospatial abilities — 2 of the most commonly affected cognitive functions in PD."

Dr. Hanganu received grants from Quebec Bio-Imaging Network and Dr. Monchi received grants from Canadian Institutes of Health Research (operating grants), Parkinson Society Canada, Fonds de la Recherche du Quebec Santé, Natural Sciences and Engineering Research Council of Canada, Canadian Funds for Innovation (equipment subsidies). Dr. Apostolova has disclosed no relevant financial relationships.

3rd World Parkinson Congress (WPC). Abstract #P15.09. Presented October 2, 2013.

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