How does brain structure change in early Parkinson's disease?
Newly diagnosed Parkinson's patients with mild cognitive impairment show rapid, widespread thinning of the brain's outer layer over 18 months compared to those with normal cognition.
Source
Baseline and longitudinal grey matter changes in newly diagnosed Parkinson's disease: ICICLE-PD study
Study at a glance
- Design
- Cohort — 18-month VBM follow-up of newly diagnosed PD (PD-MCI vs PD-NC) vs healthy controls
- N
- N=146 · 108 PD with baseline and follow-up (40 PD-MCI, 68 PD-NC) and 38 controls with both scans; 128 PD enrolled
- Population
- Newly diagnosed Parkinson's disease patients from North East England clinics and healthy controls
- Outcome
- Baseline and 18-month grey-matter change, including PD-MCI vs cognitively normal PD
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How does brain structure change in early Parkinson's disease?
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
108 patients with Parkinson's disease participated
Only subjects ( n = 108) with baseline and follow-up assessments were included in this study.
38 healthy controls were included
This resulted in a final sample size of 38 healthy controls with both baseline and follow-up scans.
What they did
The researchers tracked grey matter changes in 108 newly diagnosed Parkinson's disease patients and 38 healthy controls over an 18-month period. Using high-resolution 3 T MRI scans, they measured cortical thickness and subcortical brain volumes at baseline and follow-up. The Parkinson's group was classified into 68 patients with normal cognition and 40 with mild cognitive impairment based on scoring 1.5 standard deviations below average on cognitive tests.
What they found
At the start of the study, patients with mild cognitive impairment already had notable brain thinning in frontal, parietal, and occipital regions, alongside smaller volumes in the hippocampus and nucleus accumbens. Over 18 months, these patients experienced accelerated thinning in the frontal and temporal lobes, as well as rapid shrinkage of the caudate and hippocampus. Meanwhile, patients with normal cognition at baseline did not show early differences compared to healthy controls, but they still developed significant thinning in frontal regions over 18 months.
The limits
What it doesn't show
While the study shows clear structural differences over 18 months, it cannot prove that cortical thinning directly causes cognitive decline, as the relationships are correlational. Additionally, because the participants were evaluated while taking their normal dopaminergic medications, the potential masking effects of these drugs on cognitive scores and brain activity cannot be completely ruled out. The study is also limited by having only a single test to assess visuospatial function, which may have restricted its ability to fully capture this specific cognitive domain.
Key terms
- Parkinson's disease mild cognitive impairment (PD-MCI)
- A stage of cognitive decline in Parkinson's disease that is more pronounced than normal aging but does not yet interfere significantly with daily independence.
- Cortical thickness
- A measure of the thickness of the cerebral cortex, which represents the brain's outer layer of grey matter.
- Voxel-based morphometry (VBM)
- A neuroimaging analysis technique that allows investigation of focal differences in brain anatomy, particularly grey matter volume.
- Hippocampus
- A subcortical brain structure critical for memory formation and spatial navigation, which is often affected in neurodegenerative diseases.
- Nucleus accumbens
- A subcortical brain region involved in reward processing, motivation, and cognitive functions.
- Caudate nucleus
- A subcortical structure of the basal ganglia involved in motor control and learning, which receives extensive dopaminergic projections.
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Which left hemisphere subcortical structures were significantly atrophic in PD-MCI compared to PD-NC at baseline?
Common questions
How is mild cognitive impairment (MCI) diagnosed in Parkinson's disease patients?
Diagnoses are made using a comprehensive battery of cognitive tests, where patients must score at least 1.5 standard deviations below normal.
Does brain thinning happen before clinical cognitive symptoms appear?
Yes, the study found that Parkinson's patients with normal cognition at the start still developed significant frontal brain thinning over the 18-month period, suggesting structural changes precede detectable cognitive decline.
Were the brain scans performed while patients were on medication?
Yes, patients were assessed while taking their regular dopaminergic medications to reflect standard clinical conditions and their best functioning states.
Did any patients with normal cognition develop cognitive impairment during the study?
Yes, out of the 66 patients who started with normal cognition, 17 converted to mild cognitive impairment by the 18-month follow-up.
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