Background/Purpose: There is a lack of standardized methodology for assessing whole body MRI (WBMRI) in idiopathic inflammatory myopathy (IIM) patients. This leads to difficulty in comparing results across studies and combining data in meta-analysis.  The goal of this study was to develop a new standardized assessment tool to characterize WBMRI findings in IIM patients.  

Methods: Thirty patients with probable or definite Bohan and Peter juvenile or adult dermatomyositis (JDM, DM) or juvenile or adult polymyositis (JPM, PM) or definite IBM by Grigg’s criteria underwent WBMRI, including T1, T2, and STIR MRI sequences. A tool was developed to record scores for these patients based on consensus opinion among radiologists with expertise in musculoskeletal assessment and rheumatologists with myositis expertise.  Images were scored in a blinded manner across 34 compartments (Fig. 1) by 3-4 radiologists without an expertise in musculoskeletal disease. Each compartment was assessed for abnormal findings in muscle, subcutaneous tissue, and myofascia. The intensity of muscle signal abnormality (STIR intensity score), extent of muscle inflammation (STIR involvement score) and fatty infiltration (T1 fatty infiltration score) were scored using a 0-3-point scale. The presence of fasciitis and subcutaneous tissue signal intensity (Skin/SC T2 signal) and muscle atrophy (T1 atrophy) were evaluated on a binary scale (0=negative; 1=positive signal abnormality).

Clinical assessments included physician global disease activity visual analogue scale (PGA), the Myositis Disease Activity Assessment tool (MDAAT) and manual muscle testing (MMT). Interrater reliability was assessed by intra-class coefficient.  Correlations were assessed by spearman correlation coefficient.

Results: Patients included 12 JDM, 2 JPM, 9 DM, 4 PM, and 3 IBM. Most patients were female (80%) and 25 patients (83%) were non-Hispanic Caucasians, 3 (10%) were non-Hispanic African-Americans, and 2 (7%) had Hispanic ethnicity. The median age at the time of MRI was 26 years (IQR: 12 – 55), and the median duration between IIM diagnosis and MRI was 12.7 months (IQR: 6.7 – 23.3). There was fair to excellent agreement for 29/34 compartments (ICC>0.40). Among all IIM patients, PGA correlated with adjusted global total muscle and total disease WBMRI scores (r_s=-0.525, P=0.005 and r_s=-0.500, P=0.008, respectively). Adjusted global total muscle and total disease scores also had significant correlations with MMT (r_s=-0.399, P=0.032 and r_s=-0.388, P=0.038, respectively). There were no significant correlations between MDAAT cutaneous disease activity and WBMRI fasciitis or subcutaneous edema scores.

Conclusion: WBMRI correlated well with physician assessment of disease activity and MMT. This assessment tool offers a reliable semi-quantitative assessment of MRI findings in IIM patients. 

Figure 1.