VP.46 Dermatomyositis-specific autoantibodies and muscle MRI findings

Abstract

To date, 5 dermatomyositis specific autoantibodies (DMSAs) have been identified. Recent studies have revealed that each DM subtype according to the positive DMSA has clinical and pathological characteristic features, which naturally raises a question whether each DM subtype has unique features also on muscle MRI. We studied muscle MRI of 125 patients who had one of the 5 DMSAs and were pathologically diagnosed with DM by sarcoplasmic MxA expression at our center from January 2009 to November 2021. A total of proximal 12 leg and 8 arm muscles were evaluated in the axial plane, in addition to fascia and subcutaneous fat (SF). For skeletal muscle, the intensity (faint or strong), distribution (diffuse, patchy, or peripheral), percent area of affected (none, below 50%, more than 50%), and the texture (honeycomb pattern, homogeneous, or heterogeneous) of high signal intensity (HSI) within each muscle were evaluated. We graded the scores 0-3 according to the percent area of HSI in fascia and the scores 0-2 according to the HSI in SF. Among 125 patients, 79 were women, 32 were children (< 18years), and the median age were 54 years. Of these patients, 42 had anti-TIF1-γ, 16 anti-Mi-2, 16 anti-MDA5, 44 anti-NXP2, and 7 anti-SAE antibodies, respectively. Anti-TIF1-γ DM was associated with peripheral distribution of HSI (97.6% vs non- TIF1-γ DM 77.1%; p < 0.01). Anti-NXP2 DM was associated with diffuse distribution of HSI (97.7% vs 76.5%; p < 0.01) and high fascia score (p < 0.05). Anti-MDA5 DM was reversely associated with diffuse distribution of HSI (31.3% vs 91.7%; p < 0.001) and honeycomb pattern (62.5% vs 99.1%; p < 0.001), while it tended to have patchy distribution of HSI (56.3% vs 31.2%; p = 0.057). All DM patients had at least one HSI area in fascia. Each DM subtype according to positive DMSA seems to have characteristic MRI features, except for anti-SAE DM whose sample number was too small in this study. Fascial edema is common among DM patients.