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 κ agreement.
Results The individual measures that best characterised inactive disease (sensitivity and specificity >0.8 and Cohen's κ >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.
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Funding Supported by grants from the European Union (contract no. QLG1-CT-2000-00514) and IRCCS G. Gaslini, Genoa, Italy. DL was the recipient of the European League Against Rheumatism (EULAR) Scientific Training Bursaries. PMM attended the PRINTO headquarter at Gaslini Hospital in Genoa (Italy) as part of her visiting professorship sabbatical. LGR was supported by the intramural research program of the National Institute of Environmental Health Sciences, National Institutes of Health.
Competing interests None.
Ethics approval Ethics approval was obtained from the ethics committees of the participating centres.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement The PRINTO database related to this project is open to further research prior to acceptance of the proposal by the PRINTO Advisory Council (www.printo.it).