磁共振扩散张量成像对肌萎缩侧索硬化症患者上运动神经元病变的定量评估意义

Magnetic resonance diffusion tensor imaging: quantitative measurements on upper motor neuron of patients with amyotrophic lateral sclerosis

目的初步探讨磁共振扩散张量成像(DTI)在肌萎缩侧索硬化症(ALS)诊断中的临床意义。方法16例有明确上运动神经元(UMN)损害体征者作为A组,4例仅有下运动神经元(LMN)损害体征者作为B组,15名健康志愿者为对照组。行轴位DTI扫描,选取感兴趣区(ROI)测量各向异性分数(FA)和平均扩散系数(ADC)。结果与对照组比较,A组内囊后肢水平FA值降低(t= 3．452,P=0．002),ADC值增大(t=2．670,P=0．012);其他ROI的FA、ADC值差异无统计学意义。与对照组比较,B组内囊后肢水平FA值有下降趋势(U=11,P=0．057);与A组比较差异无统计学意义(U=29,P=0．777)。A组内囊后肢水平FA值与ALS功能评分呈正相关(r=0．577,P=0．019),与锥体束征评分呈负相关(r=-0．．789,P=0．000),与年龄、病程、病情进展速度无相关性;ADC值与以上指标间均无相关性。结论DTI可以客观而定量地评价锥体束病变,为ALS的诊断提供有价值的信息。

Objective To explore the clinical value of MR diffusion tensor imaging （DTI） in patients with amyotrophic lateral sclerosis （ALS）. Methods Sixteen patients with signs of upper motor neuron （UMN） impairments （A group） and 4 patients with isolated lower motor neuron （LMN） signs （B group） were studied. Fifteen healthy age- and sex-matched volunteers were served as controls. All subjects underwent a DTI sequence. DTI was performed using a single shot SE-EPI with 25 non-collinear diffusion gradient directions （b = 1000 s/mm^2 ） on a 1.5-T MR system. Fractional anisotropy （FA） and averaged diffusion coefficient （ADC） were quantitatively measured in 10 regions in bilateral pyramidal and nonpyramidal tract regions, including the subcortical white matter of precentral gyrul, centrum semiovale, periventricular white matter, posterior limb of the internal capsule （PIC） , cerebral peduncle, the subcortical white matter of postcentral gyrul, frontal white matter, genu corpus callosum, splenium corpus callosum and dorsal thalamus. Results In group A, FA decreased （ t = 3. 452, P = 0. 002 ） and ADC increased （ t = 2. 670, P = 0. 012 ） significantly on the PIC level and there were no significant difference of both FA and ADC among other ROIs, compared with those in the control group. In group B, there was a tendency of decrease of FA on the PIC level compared with the controls （ U = 11, P = 0. 057 ） and no significant difference compared with group A （U=29,P =0. 777）. In group A, the FA on the PIC level positively correlated with ALS function rating scale, and negatively with the score of UMN dysfunction, whereas there was no correlation of FA with age, illness duration and disease progression rate ; and there was no correlation of ADC with all above clinical variables. When the cutoff value of FA was ≤ 0. 654, the diagnostic sensitivity, specificity and the positive predictive value were 90% , 60% and 75% , respectively. Conclusions The impairment of pyramidal tracts could be non-invasively evaluated by MR-DTI in vivo, thus providing useful information in diagnosing and further understanding ALS. It is potentially useful as a quantitative tool for monitoring the progression of UMN pathology.