Corticolimbic gray matter loss in Parkinson's disease without dementia

Background: The relationship between corticolimbic involvement and cognitive dysfunction in non-demented Parkinson's disease (PD) patients has not yet been elucidated. Objectives: To delineate involvement of the cerebral cortex and limbic structures in non-demented PD and to clarify distributional differences of gray matter loss between non-demented PD with impaired cognition (PD-CI) and without cognitive impairment (PD-NC). Methods: Operational criteria based on the Clinical Dementia Rating were used to identify PD-CI. Of 40 consecutive non-demented patients with PD, 13 were classified as PD-CI and 27 as PD-NC. Comparisons of regional gray matter volume (rGMV) were made amongst the PD-CI, PD-NC, and control groups using voxel-based morphometry. Results: Gray matter loss was found extensively in the frontal, temporal, parietal, and occipital cortices in the present non-demented patients with PD. rGMV in the medial frontal and medial occipital cortices was reduced comparably in the PD-NC and PD-CI groups. The severity of gray matter loss in the perisylvian cortices increased in order from the control, to the PD-NC, to the PD-CI groups. rGMV reduction in the lateral and orbital frontal, medial and lateral temporal, medial and lateral parietal, and lateral occipital cortices and cerebellum was found specifically in PD-CI. Conclusions: Our results suggest that corticolimbic degeneration occurs in non-demented patients with PD, and extensive involvement of the limbic and posterior cortical regions as well as the frontal cortices is associated with cognitive impairment in PD.