Introduction: With a cumulative incidence approaching 80%, Parkinson's disease dementia (PDD) is a common complication of Parkinson's disease (PD). Earlier in the disease; subtle cognitive impairments are frequent. In patients with PDD, magnetic resonance imaging (MRI) demonstrates extensive grey matter (GM) loss; however, the temporal course of such change is poorly understood. We aimed to determine whether GM atrophy was present in early PD with mild cognitive impairment (PD-MCI) compared with patients with normal cognition (PD-NC); and if it correlated with neuropsychological testing.
Methods: Attention, executive, memory, language and visuospatial functions were assessed and MCI was determined using Movement Disorder Society (MDS) criteria. Patients were considered impaired if they scored 1.5 SD below age-adjusted scores. GM volume differences were evaluated using voxel-based morphometry of GM segments from T1 weighted 3T MRI.
Results: A total of 125 patients with early PD and 50 controls participated. The mean age and disease duration of the PD patients was 66 ± 10 years and 6.2 ± 4.7 months, respectively. There were no differences in age, gender or education with controls. PD patients performed more poorly in all cognitive tests. Frequencies of impairments were memory (17.6%), executive (13.6%), attention (10.4%), visuospatial (9.6%) and language (0%). Impaired sematic fluency (SF) correlated with GM loss, there was no association between impairments in other domain-specific tests and GM volume. Of the total, 39.2% of patients were classified as PD-MCI. After correcting for age and intracranial volume, there was no significant difference in GM loss compared with PD-NC or controls.
Conclusion: GM atrophy is not prominent in early PD, either in patients with MCI or normal cognition, suggesting that GM loss occurs with disease progression. This neuro-degenerative process may be quantifiable using MRI, and its utility as a biomarker for observational and therapeutic studies warrants further investigation. The association with SF is interesting; impaired SF has been found to predict subsequent PDD.