The minimal clinically important difference of the scleroderma clinical trials consortium damage index

The Scleroderma Clinical Trials Consortium Damage Index is an index of global damage in systemic sclerosis. The objective of this study is to determine the minimal clinically important difference of the Scleroderma Clinical Trials Consortium Damage Index.

Patients in the Canadian Scleroderma Research Group registry and the Australian Scleroderma Cohort Study who completed Scleroderma Clinical Trials Consortium Damage Index scores and the SF36v2 at baseline and the first full follow-up visit were studied. To calculate the minimal clinically important difference, an anchor question came from SF36v2: "Compared to one year ago, how would you rate your health in general?." Options were: much better, somewhat better, about the same, somewhat worse and much worse. We use the "somewhat worse" or "much worse" categories to indicate those with any worsening. We used four anchor methods: receiver operating characteristic curve, change difference, regression analysis, and average change.

We studied 1672 patients. Mean disease duration was 11.4 ± 10.0 years; 62.5% had diffuse cutaneous systemic sclerosis. Baseline mean Damage Index was 5.3 ± 4.2; mean change of Damage Index over 1 year was 0.9 ± 1.8 units. The calculated minimal clinically important difference values were 1 for receiver operating characteristic method, 0.625 for change difference, 0.1879 for regression analysis, and 1.37 for average change. Omitting the regression analysis method as an outlier, the mean of the other methods was 1.

The most appropriate minimal clinically important difference for the Scleroderma Clinical Trials Consortium Damage Index is a change of ⩾ 1.0 units in the Scleroderma Clinical Trials Consortium Damage Index as is already recognized by patients as a significant change after 1 year. This can be applied to group means as well as to individuals where an ordinal change is required.