阿尔茨海默病和轻度认知障碍的大脑半球间结构连接异常:一项基于DTI的研究

Interhemispheric structural connectivity abnormalities in Alzheimer's disease and mild cognitive impairment:A DTI-based study

目的探究阿尔茨海默病(Alzheimer's disease,AD)和轻度认知障碍(mild cognitive impairment,MCI)患者的大脑半球间结构连接异常及其与认知功能和日常生活活动能力的关系。材料与方法前瞻性纳入23例AD患者(AD组)、47例MCI患者(MCI组)及37例健康对照(healthy controls,HC)者(HC组)的磁共振弥散张量成像数据。利用高分辨经胼胝体纤维束模板计算并比较通往半球间同位脑区(包括前额叶、感觉运动区、顶叶、枕叶和颞叶)的32条经胼胝体神经纤维束的2个弥散指标——分数各向异性(fractional anisotropy,FA)和平均弥散率(mean diffusivity,MD),进一步将AD组和MCI组中差异脑区的弥散指标值与蒙特利尔认知评估基本量表评分(Montreal Cognitive basic Assessment,MoCA_B)和日常生活活动能力评分(activities of daily living scale,ADL)进行相关性分析。结果与HC组相比,AD组所有经胼胝体神经纤维束的MD值显著升高(P<0.05,FDR校正),除了眶额叶、额下回眶部和腹侧运动前区的其他纤维束的FA值显著降低(P<0.05,FDR校正);MCI组半球间同位脑区经胼胝体神经纤维束的FA值及MD值与HC组的差异均无统计学意义;与MCI组相较,AD组的部分经胼胝体神经纤维束(不包括前额叶和感觉运动区的部分纤维束)的FA值和MD值差异均有统计学意义(P<0.05,FDR校正)。AD组和MCI组所有经胼胝体神经纤维束的FA值及MD值与MoCA_B评分均无显著相关,但AD组多条纤维束(包括背外侧前额叶、感觉运动区、顶叶、枕叶和颞叶的部分纤维束)的FA值及MD值与ADL评分显著相关(P<0.05,FDR校正)。结论本研究结果表明,AD患者比MCI患者的大脑半球间结构连接损伤更严重且区域更为广泛;胼胝体纤维束的半球间结构连接退变与日常生活活动能力的减退更为相关。经胼胝体神经纤维束的损伤程度可作为评估AD患者生活活动能力的重要参考指标。

Objective:To explore the structural connectivity changes through the corpus callosum in the interhemispheric homologous brain regions of Alzheimer's disease(AD)and mild cognitive impairment(MCI)and the relation with clinical cognitive function and activities of daily living.Materials and Methods:MR diffusion tensor imaging data of 23 AD patients(AD group),47 MCI patients(MCI group)and 37 healthy controls(HC group)were collected.Using the high-resolution transcallosal tract template,the fractional anisotropy(FA)and mean diffusivity(MD)of 32 transcallosal tracts connecting the interhemispheric homologous brain areas(including prefrontal lobe,sensory motor area,parietal lobe,temporal lobe and occipital lobe)among the three groups were calculated and compared.In the AD and MCI groups,water diffusion index values(FA and MD)of transcallosal tracts to the different homologous brain regions were further correlated with the basic scale of Montreal Cognitive Assessment(MoCA_B)and the scale of Activities of Daily Living Scale(ADL).Results:Compared with HC,the mean MD values of all transcallosal nerve fiber bundles in the AD group had significantly increased(P<0.05,FDR correction),and most transcallosal nerve fiber tracts of AD group(excluding the tracts to the orbital frontal,inferior frontal orbital,and ventral premotor areas)had significantly lower FA values(P<0.05,FDR correction);The mean FA values and MD values of all transcallosal nerve fiber tracts to the interhemispheric homologous brain areas in the MCI group were not significantly different from the HC group.The mean FA values and MD values of some transcallosal tracts(excluding the tracts to the prefrontal and sensorimotor areas)in the AD group were significant different from the MCI group(P<0.05,FDR correction).The mean FA values and MD values of all transcallosal nerve fiber bundles were not significantly correlated with the MoCA_B scores,but the mean FA values and MD values of multiple fiber bundles(including tracts to the dorsolateral prefrontal lobe,sensorimotor area,parietal lobe,occipital lobe and temporal lobe)were significantly correlated with the ADL scores(P<0.05,FDR correction).Conclusions:This study suggests that AD had more severe and extensive damage in the interhemispheric structural connectivity than MCI,and in AD,the degeneration of interhemispheric structural connectivity in the callosal fibers is more associated with a decline in activities of daily living.The severity of the transcallosal nerve fiber bundles damage may be used as an important reference index to assess the ability of live activities in AD.