Relationship between cognitive impairment and white-matter alteration in Parkinson’s disease with dementia: tract-based spatial statistics and tract-specific analysis

OBJECTIVES: We investigated the relationship between white-matter alteration and cognitive status in Parkinson’s disease (PD) with and without dementia by using diffusion tensor imaging. METHODS: Twenty PD patients, 20 PDD (Parkinson’s disease with dementia) patients and 20 age-matched healthy controls underwent diffusion tensor imaging. The mean diffusivity and fractional anisotropy (FA) map of each patient group were compared with those of the control group by using tract-based spatial statistics. Tractography images of the genu of the corpus callosum fibre tracts were generated, and mean diffusivity and FA were measured. RESULTS: FA values in many major tracts were significantly lower in PDD patients than in control subjects; in the prefrontal white matter and the genu of the corpus callosum they were significantly lower in PDD patients than in PD patients. There was a significant correlation between the Mini-Mental State Examination (MMSE) scores and the FA values of the prefrontal white matter and the genu of the corpus callosum in patients with PD. CONCLUSIONS: Our study shows a relationship between cognitive impairment and alteration of the prefrontal white matter and genu of the corpus callosum. These changes may be useful in assessing the onset of dementia in PD patients. KEY POINTS: • Dementia is a common and important non-motor sign of Parkinson’s disease (PD). • The neuropathological basis of dementia in PD is not clear. • DTI shows abnormalities in the prefrontal white matter in PD with dementia. • Prefrontal white matter alteration may be useful biomarker of dementia in PD.