Objective. To develop and validate a definition of minimal disease activity (MDA) in patients with juvenile idiopathic arthritis (JIA). Methods. The clinical charts of JIA patients followed over a 16-year period were reviewed to identify visits with high disease activity and MDA, defined on the basis of therapeutic decisions made by the attending physician. For each JIA activity measure recorded at the time of the visit, the cutoff value that best identified states of MDA was calculated by means of the area under the receiver operating characteristic curve analysis. A definition of MDA for oligoarthritis and polyarthritis was set up after testing the relative power of each variable in a multivariate analysis. Validation procedures included assessment of discriminant and construct validity. Results. The definition that resulted from the analyses led to establish that a state of MDA could be defined as the presence of a physician global assessment ≤2.5 cm and a swollen joint count of 0 in patients with oligoarthritis; and as the presence of a physician global assessment ≤3.4 cm, a parent global assessment ≤2.1 cm, and a swollen joint count ≤1 in patients with polyarthritis. Validation procedures demonstrated that the MDA definition had good discriminant and construct validity in the context of both observational studies and controlled trials. Conclusion. We developed a preliminary definition of MDA in patients with JIA that represents a useful treatment target state and is proposed for inclusion as an outcome measure in future observational studies and clinical trials in patients with JIA.
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