Background:No clear-cut guidelines exist about the use of diagnostic procedures for idiopathic inflammatory myopathies (IIM) and only scanty and conflicting data report the use of ultrasound (US).Objectives:We aimed to assess if grey-scale (GS) and Power Doppler (PD) US, graded with a 0-3-points-scale, may be a reliable tool in a cohort of patients affected by IIM.Methods:We prospectively collected, since July to October 2020, all patients referred to Vasculitis and Myositis clinic, Rheumatology Unit, University of Siena, for suspected IIM, as well as patients with a previous, definite diagnosis of IIM and evaluated during follow-up or referred from other centers for a second opinion. All patients underwent US examination of both thighs in axial and longitudinal scans. Edema and atrophy, both assessed in GS, and PD, were graded with a 0-3-points-scale. Spearman test was used to identify the correlations between US and clinical and serological variables.Results:A total of 18 patients was included. Four of them were evaluated twice, at baseline and within 3 months of therapy. Muscle edema was found to be directly correlated with physician global assessment (PhGA), serum myoglobin and PD and negatively with disease duration. PD score was positively correlated to PhGA and negatively to disease duration. Muscle atrophy directly correlated with Myositis Damage Index and patients’ age. The single-thigh sub-analysis evidenced a direct correlation between PD score and Manual Muscle Test.Conclusion:In our cohort, we found that edema and PD are strictly related to early, active myositis, suggesting that an inflamed muscle should appear swollen, thickened and with Doppler signal. Conversely, muscle atrophy reflects the age of the patient and the overall severity of the disease. Such findings shed a new, promising, light in the role of US in diagnosis and monitoring of IIMs.Table 1.Siena Myositis Ultrasound Grading Scale (SMUGS).Grey-scale edemaGrey-scale atrophyPower Doppler0Normal muscle echotexture with hyperechoic septa and hypoechoic muscle fibers, conserved thickness.Normal muscle echotexture, with hyperechoic septa and hypoechoic muscle fibers, conserved thickness.No PD signal.1Focal hypoechoic areas, where septa are less evident. Conserved thickness.Focal heterogeneously hyperechoic areas, where septa are thicker and more evident, and muscle fibers are thinner. Conserved muscle thickness.One or two PD signals in at least one muscle (PD vascular spots, small vessels of homogenous diameters, vessel diameters approximately not superior to fibrous intramuscular septa)2Diffuse and heterogeneous hypo echogenicity (rectus femoris as hypoechoic or more than vastus intermedius), septa diffusely less evident. Conserved thickness.Diffuse and heterogeneously hyperechoic muscle, with thicker septa and thinner muscle fibers. Conserved muscle thickness.More than 2 PD signals for each muscle (as vascular spots, small vessels of homogenous diameters, vessel diameters approximately not superior to fibrous intramuscular septa).3Diffuse and heterogeneous hypo echogenicity (rectus femoris as hypoechoic or more than vastus intermedius), septa diffusely less evident. Increased thickness (rectus femoris became thicker than vastus intermedius).Diffuse and heterogeneously hyperechoic muscle, with thicker septa and thinner muscle fibers. Reduced muscle thickness.More than 2 PD signals for each muscle with larger diameter of the vessel (at least superior to fibrous intramuscular septa), or vessels with different diameters or branched vessels.Figure 1.Different PD findings (clockwise) in longitudinal anterior scans of the thigh: PD 3 in a patient with a recent diagnosis of anti-Mi2 DM; PD 2 in the same patient after one month of treatment with steroids and Methotrexate; PD 1 in a patient affected by anti-SAE DM, with a suspected disease flare; PD 0 in a patient affected by an advanced polymyositis diagnosed in 2000, currently not in treatment.Disclosure of Interests:None declared
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