Background/Purpose: Prometheus study was a prospective, randomized, assessor-blind multicenter trial, comparing the efficacy and safety of the glucocorticoid (GC) monotherapy versus combination therapy with methotrexate (MTX) and GC in patients with polymyositis (PM) and dermatomyositis (DM). Muscle MRI has been used to assess disease activity and response to treatment. To assess MRI findings two different methods were used: semi-quantitative scoring system and quantitative assessment using manual measuring tool and picture analysis provided by TomoCon® Workstation.

Methods: For semi-quantitative assessment of edema, we used scoring 0, 1, 2, and 3 according to intensity of signal in each of the 16 thigh muscles. Muscle damage was evaluated in three basic thigh muscle compartments and pelvic muscles using Goutallier grading (0 – 5) based on extent of fatty replacement. Both sides were assessed by two evaluators, an average was made for each muscle, and values were summed up in the total score (MRI Semi-Quantitative total edema score = MRI S-Q TES).  TomoCon® software provides pixel analysis in manually selected regions of interest. Manual muscle test (MMT8) and CK were measured and patient’s global assessment (PGA), physician’s GA (PhGA) and muscle disease activity (MDA) were recorded on visual analogue scales.

Results: Seventeen patients had MR images taken before the baseline visit, 8 had also the second MRI after 3 months of therapy. There was a significant reduction of MRI S-Q TES after 3 months in patients with PM and DM (from the mean 17.4 points, SD 13.7 to 8.0 points, SD 12.3; p=0.025). No significant progression of fatty atrophy was observed (from 16.0 points, SD 8.8, to 19.4, SD 4.6; p=0.3). At baseline, a significant correlation between MRI S-Q TES and PGA was noted (p=0.027). There was also a borderline negative association of MRI S-Q TES with muscle strength evaluated by MMT 8 (p=0.053). We noted a significant association between MRI S-Q TES and MRI Quantitative total edema score (MRI Q TES) (p=0.04) as well as between semi-quantitative and quantitative edema scores comparing individual muscles (p=0.0004). There was also a borderline association of MRI S-Q TES with MRI atrophy score (p=0.061). In a subset of 8 patients with longitudinally performed two MRI evaluations we found a good correlation between initial MRI S-Q TES and the level of serum CK (p=0.028).  However, no correlation was seen between the level of improvement in MRI S-Q TES and drop in CK or with any other clinical parameters after 3 months of treatment.

Conclusion: Compared to the results of established semi-quantitative scoring method we demonstrated a good reliability of newly proposed quantitative evaluation system of muscle edema. This system was applied to record degree of muscle edema in a subpopulation of patients with PM and DM, treated in the clinical study. A significant association between MRI S-Q TES and MRI Q TES was found. Correlations of MRI scores with clinical and laboratory parameters were demonstrated.

Acknowledgements: Supported by the project (Ministry of Health, Czech Republic) for conceptual development of research organization 00023728 (Institute of Rheumatology).

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/semi-quantitative-and-quantitative-evaluation-of-magnetic-resonance-imaging-in-patients-with-idiopathic-inflammatory-myopathies-a-subanalysis-of-the-prometheus-study/