[Clinical characteristics of anti-melanoma differentiation associated gene 5 antibody-positive juvenile dermatomyositis].

To analyze the clinical characteristics of anti-melanoma differentiation associated gene 5 (MDA5) antibody-positive juvenile dermatomyositis (JDM) patients. A retrospective case-control study was conducted. The positive group included 18 children with anti-MDA5 antibody-positive JDM who were admitted to the Department of Rheumatology and Immunology at Capital Center for Children's Health with Capital Medical University between January 2016 and January 2023. Another 36 children with anti-MDA5 antibody-negative JDM hospitalized during the same period were enrolled as the negative group. Based on the extent of pulmonary involvement and pulmonary CT scores, the MDA5-positive group was further divided into severe pulmonary involvement and non-severe pulmonary involvement subgroups. Chi-square test and Kruskal-Wallis test were used to compare clinical features, laboratory test results between groups. Among the 18 patients in the MDA5-positive group, 7 were male and 11 were female, with an age of onset of 5.0 (2.6, 9.4) years and disease duration of 6.0 (4.0, 9.3) months. The MDA5-negative group included 36 cases (14 male, 22 female), with an age of onset of 4.9 (2.0, 7.0) years and disease duration of 5.0 (1.8, 7.0) months. The MDA5-positive group exhibited significantly higher rates of arthritis, skin ulcers, and interstitial lung disease (ILD), along with elevated serum ferritin (SF) and erythrocyte sedimentation rate levels compared to the MDA5-negative group (9/18 11% (4/36), 6/18 3% (1/36), 16/18 33% (12/36), 327 (141, 518) 131 (68, 257) μg/L, 17.5 (12.5, 26.8) 11.0 (5.0, 13.0) mm/1 h, ²=7.92, 7.41, 14.84, =2.50, 2.87, all 0.05). Conversely, the MDA5-positive group had lower rates of muscle weakness and lower creatine kinase levels (5/18 75% (27/36), 58.5 (49.3, 97.5) 225.0 (68.0, 695.5) U/L, ²=11.08, =-2.94, both 0.05). Severe pulmonary involvement 6 cases and non-severe pulmonary involvement subgroups 12 cases. Among the MDA5-positive patients, those in the severe pulmonary involvement subgroup had an older age at onset and higher rates of muscle weakness as well as hydroxybutyrate dehydrogenase (HBDH), lactate dehydrogenase (LDH), SF, and Krebs von den Lungen-6 (KL-6) compared to the non-severe subgroup (all 0.05). In the MDA5-positive group, 17 patients improved after treatment with glucocorticoids combined with immunosuppressants, while One died due to rapidly progressive ILD. Anti-MDA5 antibody-positive JDM is characterized by typical skin rashes, a high incidence of arthritis and skin ulcers, relatively mild muscle involvement, but is prone to ILD. Among MDA5-positive patients, those with older age at onset, muscle involvement (manifested as muscle weakness and elevated muscle enzymes (LDH, HBDH)), or significantly elevated KL-6 and SF levels are more likely to develop severe pulmonary complications.