Myositis Assessment Tool is Reliable and Valid

The Myositis Disease Activity Assessment Tool, with improvements made with modification, appears to be a reliable and valid instrument for assessing myositis disease activity. The tool represents the first major attempt to assess the reliability and validity of an activity index in myositis.

Sultan and associates conducted an international, prospective, cross-sectional, multicenter study of patients with probable or definite myositis in 2 phases; the tool was modified for use in the second phase of the reliability study. Two activity indices, the Myositis Intention-to-Treat Activity Index (MITEX) and the Myositis Disease Activity Assessment Visual Analog Scales, were used to evaluate the constitutional, cutaneous, skeletal, cardiac, pulmonary, GI, and muscle organ systems. Interrater reliability was assessed, and criterion validity was measured.

Interrater reliability improved in the second phase of the study, and the validity of the assessment tool improved significantly after modification. Overall sensitivity, specificity, and positive predictive value (PPV) improved from 86%, 92%, and 67%, respectively, in the first phase to 96%, 94%, and 83%, respectively, in the second phase. Correlation between the 2 instruments for individual systems was good.

The authors noted that use of the tool will require formal training and a computerized version of this index, currently being developed, should allow for ease of scoring.