DTI reflects symptomatology and discriminates Parkinson's from Alzheimer's MCI and normal controls

The cognitive profile in early Parkinson's disease (PD) differs from that in Alzheimer's disease (AD). The underlying mechanisms are unknown. Very few studies have explored whether the integrity of white matter (WM) is associated with cognition in PD. Our objective was to u se MRI diffusion tensor imaging (DTI) to test the hypotheses that 1) decreased WM integrity is associated with early cognitive impairment in PD, and 2) that WM integrity is differentially reduced in PD- and AD-MCI, putatively reflecting differences in symptomatology. Consecutive patients diagnosed with PD were recruited if they had no dementia, duration of disease < 5 years, Hoehn Y Hahr < 2.5. Patients with MCI due to AD and normal elderly controls (NC) were included. Standardized rating scales and neuropsychological tests were administered, and MRI scans (1.5T) performed DTI white-matter ROIs including those typically affected in AD (temporal), putatively in PD (middle frontal lobe and occipital cortex) were included, and nigro-striatal tracts were identified and included, age and sex regressed out. Data on the first 10 PD and MCI patients and 20 NC are presented, using Anova linear trends and planned contrasts. Demographics did not differ between groups. DR in nigral-adjacent WM ROIs increased from NC to AD to PD (linear trend p=0.005). There were significant differences in temporal and occipital WM ROIs. For DR in the left enthorhinal cortex; NC ‰ PD < AD (contrasts p=0.001), whereas in the right; NC < AD < PD (linear trend p=0.011). DR in right occipital ROIs were higher in PD. In the lingual cortex NC < PD (contrasts p= 0.001), and increased from NC to AD to PD (linear trend p=0.001).ROIs and cognition: Analysis of associations between cognitive domains and DTI in the groups is ongoing and will be presented at the meeting. White-matter integrity is affected in PD-MCI and differs from findings in MCI-AD in a pattern consistent with typical cognitive profiles.