Background/Purpose:

Musculoskeletal MRI represents a valuable non-invasive technique for dectecting muscle inflammation in idiopathic inflammatory myopathies (IIM). So far, all MRI studies in juvenile dermatomyositis (JDM) have focused on the thighs muscles. Whole-body MRI (WB-MRI) is a new technique which allows to screen the entire muscular-skeletal system and gives a complete assessment of the total inflammatory burden in patients with IIM. However, its potential in children with JDM has never been explored so far. Purpose: to evaluate the contribution of WB-MRI examination in the clinical assessment of JDM patients and to investigate its feasibility and validity in the assessment of disease activity.

Methods:

WB-MR images were obtained from 30 JDM patients (12M;18F,median age 8.6 years) and from 30 children (13M; 17F, median age 10.4 years) without inflammatory myopathies (control group), using a 1.5 Tesla and Short Tau Inversion Recovery (STIR) sequences. Signal intensity was scored using a 0-2 point scale in 42 muscular groups; myofascial and subcutaneous tissue inflammation were assessed on the upper and lower extremities using a 0-1 point scale. Validation procedures included the analysis of reliability, construct validity, discriminant validity and sensitivity to change.

Results:

in addition to a symptomatic proximal distribution of inflammation, WB-MRI revealed asymptomatic distal legs muscle inflammation in 19 out of 30 patients(70%) and asymptomatic forearms inflammation in 15 out of 30 patients (50%). Twenty-three patients showed a typical patchy and heterogeneous distribution of muscular inflammation. In 3 patients the abnormal hyperintense areas tended to be diffusely and homogeneously distributed within the muscles. WB-MRI showed inactive disease in 4 patients. Fascial and subcutaneous tissue inflammation were detected in 9 out of 30 (30%) and 18 out of 30 (60%) patients, respectively. WB-MRI scores were significantly increased in active JDM when compared with the inactive JDM group (p=0.02) and the control group (p<0.0001), indicating an excellent discriminant validity of the WB-MRI. The inter- and intra-reader agreement for the muscular, subcutaneous and fascial WB-MRI scores were excellent (intra-class correlation coefficient >0.8). The muscular WB-MRI score showed moderate to excellent correlations with indicators of disease activity such as the Manual Muscle Test (MMT;rs=0.86), the Childhood Myositis Assessment Scale (CMAS;rs=0.85) and physician’s assessment of disease activity (VAS Phys;rs=0.75). WB-MRI score showed a higher responsiveness to change (standardized response mean=0.86) compared to MMT (SRM=0.51), CMAS (SRM=0.28), VAS Phys (SRM=0.63) and CPK (SRM=0.17).

Conclusion:

WB-MRI provides additional information to the clinical assessment by revealing a wider involvement of muscle groups and different patterns of distribution of muscle inflammation. WB-MRI score allows to reliably visualize the extent of the inflammatory process and therefore it represents a promising non-invasive tool to estimate the total disease burden, to adjust treatment to disease severity and to monitor treatment efficacy in JDM.

 

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/role-of-whole-body-magnetic-resonance-imaging-in-the-assessment-of-disease-activity-in-juvenile-dermatomyositis-a-pilot-study/