Objective: To test the reliability, discriminating validity and clinical value of myositis disease activity tool in Chinese patients with polymyositis/dermatomyositis (PM/DM).
Methods: Fifty-four PM/DM patients (PM, n = 18; DM, n = 36) at our hospital between January 2009 and June 2010 were enrolled into this prospective study. The disease activity was assessed by the MDAAT (myositis disease activity assessment tool). The reliability and discriminating validity were assessed with test-retest reliability, interrater reliability and t-test analysis.
Results: The reliability analysis of MDAAT indicated 8 items (constitutional, cutaneous, skeletal, gastrointestinal, pulmonary, cardiovascular, muscular & global) had excellent reliability, the ICC (intraclass correlation coefficient) was 0.72 (95%CI: 0.57, 0.83), 0.88 (95%CI: 0.79, 0.93), 0.83 (95%CI: 0.72, 0.90), 0.62 (95%CI: 0.42, 0.76), 0.81 (95%CI: 0.70, 0.89), 0.59 (95%CI: 0.38, 0.74), 0.85 (95%CI: 0.75, 0.91) and 0.84 (95%CI: 0.73, 0.90) respectively. MDAAT had excellent discrimination validity in all items except for cardiovascular ones.
Conclusion: With excellent reliability and discriminating validity, MDAAT may be used to assess the disease activity and therapeutic effects of Chinese PM/DM patients.