Comparison of disease severity and activity between juvenile- and adult-onset dermatomyositis: a multicenter cohort study

Objectives To compare the severity at diagnosis and disease activity during follow-up between juvenile (jDM) and adult-onset dermatomyositis (aDM). Methods Patients with DM fulfilling the 2017 ACR/EULAR criteria and tested for myositis-specific antibodies were included. Overall severity at diagnosis was defined by at least one of the following: severe muscle impairment, symptomatic interstitial lung disease (ILD), gastrointestinal (GI) vasculitis, myocarditis, severe skin ulceration, or admission to an intensive care unit. Clinically inactive disease and remission were defined according to PRINTO group criteria and IMACS guidelines. Results 201 patients were included: 123 with aDM (≥ 18 years) and 78 with jDM (< 18 years). Female predominance was less pronounced and GI involvement was more frequent in jDM. Anti-NXP2 antibodies (Abs) were more frequent in jDM. Severe disease at diagnosis was present in 44% of cases, with symptomatic ILD more common in adults and GI vasculitis more common in children. No difference was observed in severe muscle disease. In jDM, anti-NXP2 Abs (OR = 6.29 [2.00–23.07], p= 0.003) and joint involvement (OR = 3.44 [1.33–11.47], p= 0.03) were associated with severe disease at diagnosis, while in aDM, anti-Mi2 Abs were associated with a lower likelihood of severe disease (OR = 0.12 [0.02–0.42], p= 0.003). No significant difference was observed in clinically inactive disease or remission at the last follow-up. Severe infections occurred in 25% of patients. Conclusion Severity profiles differ by age of DM onset. Autoantibodies are key indicators of severity at diagnosis in both juvenile DM and adult DM.