The PRINTO criteria for clinically inactive disease in juvenile dermatomyositis

Objectives To develop data-driven criteria for clinically inactive disease on and off therapy for juvenile dermatomyositis (JDM). Methods The Paediatric Rheumatology International Trials Organisation (PRINTO) database contains 275 patients with active JDM evaluated prospectively up to 24 months. Thirty-eight patients off therapy at 24 months were defined as clinically inactive and included in the reference group. These were compared with a random sample of 76 patients who had active disease at study baseline. Individual measures of muscle strength/endurance, muscle enzymes, physician's and parent's global disease activity/damage evaluations, inactive disease criteria derived from the literature and other ad hoc criteria were evaluated for sensitivity, specificity and Cohen's kappa agreement. Results The individual measures that best characterised inactive disease (sensitivity and specificity >0.8 and Cohen's kappa >0.8) were manual muscle testing (MMT) >= 78, physician global assessment of muscle activity = 0, physician global assessment of overall disease activity (PhyGloVAS) <= 0.2, Childhood Myositis Assessment Scale (CMAS) >= 48, Disease Activity Score <= 3 and Myositis Disease Activity Assessment Visual Analogue Scale <= 0.2. The best combination of variables to classify a patient as being in a state of inactive disease on or off therapy is at least three of four of the following criteria: creatine kinase <= 150, CMAS >= 48, MMT >= 78 and PhyGloVAS <= 0.2. After 24 months, 30/31 patients (96.8%) were inactive off therapy and 69/145 (47.6%) were inactive on therapy. Conclusion: PRINTO established data-driven criteria with clearly evidence-based cut-off values to identify JDM patients with clinically inactive disease. These criteria can be used in clinical trials, in research and in clinical practice.