Responsiveness of fibromyalgia clinical trial outcome measures

To assess the responsiveness of the Fibromyalgia Impact Questionnaire (FIQ), patient ratings of pain intensity, number of tender points, and total tender point pain intensity score to perceived changes in clinical status in patients with fibromyalgia (FM).

Using data from a randomized placebo controlled study evaluating efficacy of magnetic therapy in patients with FM, the ability of primary outcomes to detect clinically meaningful changes over a 6 month period was assessed by: (1) degree of association between outcome change scores and patient global ratings of symptom change (Spearman rank-order correlations); (2) ability of these scores to discriminate among groups of patients whose perceived health status had changed to varying degrees (ANOVA); (3) ability of these scores, individually and jointly, to discriminate between patients who had reported improvement and those who did not (logistic regression); (4) effect size, standardized response mean, and Guyatt's statistic were calculated to quantify responsiveness.

Correlations showed the outcome measures were moderately responsive to perceived symptomatic change. For FIQ, pain intensity ratings and number of tender points, differences in change scores between globally improved and unchanged groups and between globally improved and worsened groups were significant; for total tender point pain intensity, the globally improved differed from worsened group. FIQ outperformed the other measures in discriminating between patients who reported improvement from those who did not. Summary statistics were consistent with discriminatory analyses, indicating the measures were sensitive to improvement, but relatively unresponsive to decline.

The FIQ was the most responsive measure to perceived clinical improvement and we recommend its inclusion as a primary endpoint in FM clinical trials.