Study On The Microstructural Differences Of White Matter In Different Subtypes Of Mild Cognitive Impairment Based On Diffusion Tensor Imaging

Objectives: Vascular mild cognitive impairment(VaMCI)and amnestic mild cognitive impairment(aMCI)are the two most common types of mild cognitive impairment(MCI).Previous studies have shown white matter(WM)abnormalities in the two MCI.However,whether they differ to each other haven't been proven.This study was designed to directly examine whether and how white matter(WM)microstructure differs in the two MCI subtypes,Methods: This study included sixty-three right-handed participants: twenty-eight VaMCI(12 males,age range: 46~77 years),thirty-four aMCI patients(14 males,age range: 51~79 years).All patients underwent a battery of neuropsychological tests and structural and diffusion magnetic resonance imaging(MRI)scanning.WM microstructure was quantified using diffusion MRI parameters: fractional anisotropy(FA),mean diffusivity(MD),axial diffusivity(AxD)and radial diffusivity(RD).These parameters were compared between the two patient groups using tract-based spatial statistics(TBSS)after controlling for age,gender,and education.The interaction between the FA and cognitive scores was also evaluated using a general linear model(GLM).Results: Compared with standard brain,both the two subtypes have a spread WM impairment.However,no significant differences in FA/MD/AxD/RD were observed between the VaMCI and a MCI groups,which suggests a similar pattern of WM microstructure changes in the early stage of cognitive impairment for different dementia sub-types.However,the two groups exhibited significant differences in the relationship between FA and the Auditory Verbal Learning Test(AVLT),which were primarily located around the regions such as corona radiate and corpus callosum.Specifically,there were significant positive correlations(R = 0.64,P < 0.001)between the FA and AVLT in the VaMCI group,but the opposite trend was observed in the aMCI group(R =-0.34,P = 0.047).Conclusions: The two MCI are at the same cognitive impairment stage,but have a different episodic memory defect.Despite the cause difference for dementia,WM microstructure showed a similar pattern in the early stage,e.g.,VaMCI and aMCI.However,the WM-memory relationship already differed between VaMCI and aMCI,suggesting an independent neuropathology for specific memory deficits in different types of dementia.