Disease Activity and Prognostic Factors in Juvenile Dermatomyositis: a Long-term Follow-up Study Applying the Paediatric Rheumatology International Trials Organization Criteria for Inactive Disease and the Myositis Disease Activity Assessment Tool

Objectives: The aims of this study were to examine disease activity by the Paediatric Rheumatology International Trials Organization (PRINTO) criteria for inactive disease and the Myositis Disease Activity Assessment Tool (MDAAT) in JDM patients after long-term follow-up and to identify predictors of these outcomes.

Methods: A retrospective inception cohort of 59 patients diagnosed with JDM was clinically examined in a cross-sectional study a median of 16.8 years (range 2.0-38.1) after symptom onset. Patients were divided by the PRINTO criteria into clinically inactive and active disease. Disease activity was also measured by MDAAT and other validated tools. Medical records were reviewed for early disease variables and medication.

Results: By the PRINTO criteria, 31/59 (51%) patients were active and 29/59 (49%) were inactive. By MDAAT, 43/59 (73%) of the patients had measurable disease activity, most commonly found in the skin (59%) and skeletal (27%) systems. MDAAT showed moderate to strong correlations with other disease activity measures (rsp 0.39-0.87, P < 0.05) except for muscle enzymes. Active patients had higher disease activity than inactive patients measured by MDAAT (P < 0.001) and other disease characteristics (all P ≤ 0.002) except for patients' global assessment of disease activity. After controlling for gender and follow-up time, calcinosis during disease-course predicted high MDAAT, age<9 years at diagnosis predicted active disease and organ damage present 6-12 months post diagnosis predicted both outcomes.

Conclusion: After 16.8 years, 51-73% of JDM patients had active disease. Disease activity by the PRINTO criteria and MDAAT were moderately to highly associated with most other disease characteristics and was predicted by early damage.