The value of quantitative muscle ultrasound in monitoring muscle and fascia inflammatory activity in juvenile dermatomyositis patients.

Background: Currently, the activity of juvenile dermatomyositis (JDM) is mainly assessed based on clinical manifestations, creatine kinase (CK) level, and magnetic resonance imaging (MRI), but certain limitations arise in these approaches for children. Thus, this cross-sectional study aimed to explore the value of ultrasound in evaluating muscle inflammation via the dynamic analysis of muscle ultrasound characteristics in children with active or stable JDM.

Methods: The data of a group of children who were diagnosed with JDM and admitted to the Rheumatology and Immunology Department of the Capital Pediatric Research Institute Children's Hospital between June 2022 and November 2023, and a normal control group were collected. The clinical, ultrasound, and laboratory data of the children with active and stable JDM were collected and compared with those of a normal control group. Muscle thickness (MT), fascia thickness (FT), muscle echo intensity (EI), muscle microvascular flow imaging (MVFI) distribution, and the blood flow resistance index (RI) were measured via ultrasound for the comparative analysis. A Spearman correlation analysis was conducted to assess the correlation between the ultrasound parameters in the JDM patients, and muscle scores and laboratory indicators of disease activity. Receiver operating characteristic (ROC) curves were generated for the ultrasound parameters. Five active JDM children were dynamically followed up.

Results: The data of 26 children with active JDM, 29 with stable JDM, and 31 normal control children were collected. The patients with active JDM had significantly greater EI (median 68.9 47.4, P<0.01), increased FT (median 0.25 0.15, P<0.01), and an increased MVFI distribution (P<0.01). The Spearman correlation analysis revealed a negative correlation between increased EI, FT, and MVFI distribution, and the Childhood Myositis Assessment Scale (CMAS) score (R=-0.662, -0.673, -0.667, all P<0.05). There was a statistically significant difference in EI between the stable JDM children and healthy children (median 47.4 39.0, P<0.05). During the follow-up period, two children with slow fasciitis resolution developed soft tissue calcification.

Conclusions: EI, FT, and MVFI distribution can be used to assess the activity status of individuals with JDM, and are correlated with clinical activity indices. EI may be abnormal even in children with a stable clinical condition, which suggests that ultrasound may more accurately reflect muscle status. Children with long-term unresolved fasciitis may be at risk of developing calcification.