Application Of DTI And T2-mapping In The Assessment Of Polymyositis And Dermatomyositis

ObjectiveIn this study,DTI and T2-mapping imaging were used to quantitatively evaluate the microscopic changes in edema and "normal" areas shown by routine MRI of thigh muscle in PM/DM patients,as well as to investigate the correlation between measurement parameters of DTI and T2-mapping and serum CK and MMT scores.ROC curve was applied to predict the diagnostic effect of T2 value of thigh muscle in edematous muscle and uninvolved part,non-edematous muscle and control group.Overall,the ultimate goal of this paper was to explore the application value of DTI and T2-mapping in clinical evaluation and diagnosis of thigh muscle involvement in PM/DM patients,and to provide basis for early clinical evaluation,diagnosis and intervention.Subjects and MethodsTwenty-one patients diagnosed with PM/DM in the Department of Rheumatology of our hospital from October 2018 to October 2020 were selected as the case group along with twenty-one healthy control subjects,including 9 patients diagnosed with PM and 12 patients diagnosed with DM.Both groups were scanned by conventional MRI,DTI and T2-mapping sequences of bilateral thigh muscles.According to the conventional MR images,the thigh muscles of PM/DM patients were divided into three groups,the involved part of edema muscle mass,the uninvolved part of edema muscle mass,and the group without edema muscle mass.The ADC,FA and T2 values of each group were measured.The independent sample t-test was used to compare patients with controls in ADC,FA and T2 values.The Games-Howell test was used to analyze the difference in T2 value among the muscles of non-edema group.The correlation of between T2 values and clinical indicators was analyzed by the spearman coefficient correlation,as well as the ROC curve was constructed based on T2 value.Results1.PM/DM patients showed significantly higher ADC and T2 values in thigh muscle than controls.Considering the Vastus lateralis,Gracilis and Semimembranosus muscles,there was no statistical difference of FA value between the groups(P>0.05),while the others showed statistically significant differences(P<0.05).2.There was no significant difference in T2 value of edema muscle in anterior,posterior and medial thigh muscles in PM/DM patients(P > 0.05).T2 values of the non-edema muscle group were obtained that anterior muscle was 4.46 ms higher than the medial muscle along with 4.45 ms higher than the posterior muscle with statistical significance(P < 0.05).3.The T2 relaxation time of PM/DM patients and the MMTs was highly negative correlated(r=-0.884,P<0.01).The T2 relaxation time and the serum CK levels was moderate positive correlated(r=0.622,P<0.01).The serum CK levels and the MMTs was moderate negative correlated(r=-0.564,P<0.01).4.When the T2 threshold was set at 44.65 ms for the distinction from the controls,the area under the curve was 0.997,Youden index was 0.935,and the sensitivity and specificity were 94.9% and 98.6% respectively.When the T2 threshold was set at 73.55 ms,the area under the curve for differentiating the involved part from the uninvolved part of the edematous muscle was 0.962,a statistically significant result(P<0.05)with Youden’s index,sensitivity,and specificity of 0.824,92.1%,and 90.3% respectively.Conclusion1.The vastus lateralis muscle and the rectus femoris muscle were significantly more affected in PM/DM patients,and the vastus lateralis inflammatory changes were most pronounced in muscles without edema.2.The ADC and T2 values were significantly increased in edema muscle compared with non-involved muscle group and the controls,while FA values were significantly lower oppositely.3.The ADC and T2 values of the uninvolved part of the edema muscle in PM/DM patients were higher than those in the normal control group.4.The T2 value of PM/DM patients were highly negatively correlated with the MMT score,which was a moderate positive correlation with serum CK value.5.The diagnostic sensitivity and specificity were 94.9% and 98.6% when the T2 threshold between PM/DM patients and the control was set at 44.65 ms.The diagnostic sensitivity and specificity were 92.1% and 90.3% when the T2 threshold between the involved and uninvolved portions of the edema muscle in PM/DM patients was set at 73.55 ms.