Cortical Thinning and Cognitive Function in Early Parkinson’s

VBCN - July 2014 Volume 1, No 2

Results of the largest study to evaluate the link between cognition and cortical thinning using 3T magnetic resonance imaging (MRI) show cortical thinning in patients with early-stage Parkinson’s disease (PD) that is associated with mild cognitive impairment (MCI) as reflected by lower cognitive function scores. This finding could lead to earlier diagnosis and treatment of PD, the researchers note (Pereira JB, et al. Neurology. 2014;82:2017-2025).

Other studies had already shown that “early MCI is associated with an increased risk of developing dementia in PD,” noted lead author Joana B. Pereira, PhD, with the Karolinska Institutet, Stockholm. “In this study, we showed that newly diagnosed, drug-naïve PD patients with MCI had cortical thinning in temporal, parietal and frontal regions already at early disease stages. This could serve as a marker of initial cognitive decline in PD.”

Keith A. Josephs, MD, Professor of Neurology, Mayo Clinic, Rochester, MN, told Value-Based Care in Neurology that the study adds to “an already substantial literature” linking MCI in PD with significant neurodegeneration in the brain.

“The findings help shed light on the neurobiological underpinnings of cognitive dysfunction in PD, and may ultimately allow the development of neuroimaging biomarkers that could be useful for assessing future treatment,” said Dr Josephs.

The 123 patients with PD and 56 controls without PD were part of the Parkinson’s Progression Markers Initiative. The patients with PD had been diagnosed within the previous 2 years and had not been treated for the disease.

Of the 123 patients with PD, 33 showed evidence of MCI based on the modified Movement Disorder Society (MDS) Task Force definition (PD-MCI-MDS). In addition, 18 patients were classified as having MCI based on their cognitive domain scores (PD-MCI-Domain). In all, 16 individuals had MCI according to both definitions.

The 3T MRI scans revealed cortical thinning in the right inferior temporal gyrus in patients with PD who were cognitively normal (PD-CN) compared with the controls, when the researchers used the PD-MCI-MDS

definition (this difference was not present when they used the PD-MCI-Domain). Furthermore, thinning in this region was present in patients with PD-MCI, using both definitions, compared with the controls, and this group also had even more thinning in the left inferior temporal gyrus.

The novelty of this study is the assessment of treatment-nave patients with PD at the earliest stages of cognitive impairment. “The regional cortical thinning in PD-CN patients we observed suggests that cortical changes are already present at time of diagnosis, before meeting criteria for MCI,” Dr Pereira and colleagues note. The cortical changes finding in patients with PD-CN “suggest to be a preclinical biomarker of cognitive decline even in patients with normal cognition at baseline,” they emphasize.

In addition, the researchers found correlations between higher visuospatial scores and thicker bilateral superior parietal, left-hemisphere temporal, and precentral regions. Moreover, the executive attention domain scores were correlated with cortical thickness in a number of regions, including the superior frontal, precentral, temporal, and parietal areas.

Performance in the verbal encoding memory subtest correlated with increased thickness in the middle, superior, and inferior temporal areas in both hemispheres. There were no significant correlations between thickness and delayed recall scores or disease duration.

These study results show “that better scores on cognitive tests are associated with greater cortical thickness in patients,” said Dr Pereira.

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