Lee D Y, Fletcher E, Martinez O, Ortega M, Zozulya N, Kim J, Tran J, Buonocore M, Carmichael O, DeCarli C
Imaging of Dementia and Aging (IDeA) Laboratory, Department of Neurology and Center for Neuroscience, University of California at Davis, Davis, CA 95616, USA.
Neurology. 2009 Nov 24;73(21):1722-8. doi: 10.1212/WNL.0b013e3181c33afb. Epub 2009 Oct 21.
To cross-sectionally compare the regional white matter fractional anisotropy (FA) of cognitively normal (CN) older individuals and patients with mild cognitive impairment (MCI) and Alzheimer disease (AD), separately focusing on the normal-appearing white matter (NAWM) and white matter hyperintensities (WMH), and to test the independent effects of presumed degenerative and vascular process on FA differences.
Forty-seven patients with AD, 73 patients with MCI, and 95 CN subjects received diffusion tensor imaging and vascular risk evaluation. To properly control normal regional variability of FA, we divided cerebral white matter into 4 strata as measured from a series of young healthy individuals (H1 = highest; H2 = intermediate high; H3 = intermediate low; H4 = lowest anisotropy stratum).
For overall cerebral white matter, patients with AD had significantly lower FA than CN individuals or patients with MCI in the regions with higher baseline anisotropy (H1, H2, and H3), corresponding to long corticocortical association fibers, but not in H4, which mostly includes heterogeneously oriented fibers. Vascular risk showed significant independent effects on FA in all strata except H1, which corresponds to the genu and splenium of the corpus callosum. Similar results were found within NAWM. FA in WMH was significantly lower than NAWM across all strata but was not associated with diagnosis or vascular risk.
Both vascular and Alzheimer disease degenerative process contribute to microstructural injury of cerebral white matter across the spectrum of cognitive ability and have different region-specific injury patterns.
横断面比较认知正常（CN）的老年人、轻度认知障碍（MCI）患者及阿尔茨海默病（AD）患者脑白质各区域的分数各向异性（FA），分别聚焦于外观正常的白质（NAWM）和白质高信号（WMH），并检验假定的退行性和血管性病变过程对FA差异的独立影响。
47例AD患者、73例MCI患者及95例CN受试者接受了扩散张量成像及血管风险评估。为恰当控制FA的正常区域变异性，我们将脑白质根据一系列年轻健康个体的测量结果分为4层（H1 = 最高；H2 = 中等偏高；H3 = 中等偏低；H4 = 各向异性最低层）。
对于全脑白质，AD患者在基线各向异性较高的区域（H1、H2和H3，对应长皮质 - 皮质联合纤维）的FA显著低于CN个体或MCI患者，但在主要包含方向各异纤维的H4层并非如此。血管风险在除H1（对应胼胝体膝部和压部）外的所有层对FA均有显著独立影响。在NAWM中也发现了类似结果。WMH中的FA在所有层均显著低于NAWM，但与诊断或血管风险无关。
血管性病变和阿尔茨海默病退行性病变过程均导致认知能力范围内脑白质的微观结构损伤，且具有不同的区域特异性损伤模式。
