Comparison of the validity and sensitivity to change of 5 activity indices in systemic lupus erythematosus

To compare the construct validity and sensitivity to change of the Systemic Lupus Activity Measure (SLAM), Systemic Lupus Erythematosus Disease Activity Index (SLEDAI), Lupus Activity Index (LAI), British Isles Lupus Assessment Group index (BILAG), and the European Consensus Lupus Activity Measure (ECLAM).

Twenty-three patients with systemic lupus erythematosus (SLE) were examined prospectively every 2 weeks for up to 40 weeks. Nineteen patients completed all 20 assessments. At each assessment, each of the 5 activity indices was scored, along with physicians' and patients' global assessments of SLE activity. Construct validity was determined by the strength of correlations between changes over time in each activity index and changes in physician and patient global assessments. Sensitivity to change was determined by the magnitude of change in each index over the 2 week interval of greatest change in the physician or patient global assessments, and calculated as standardized response means (SRM; mean change/standard deviation of change). Thirteen patients were also examined monthly by a second physician who was blinded to previous scores on the activity indices and to the patient global assessments.

Patients had substantial changes in SLE activity during the study. Changes in each activity index were correlated with changes in the physician global assessment (SLAM r = 0.54; SLEDAI r = 0.52; LAI r = 0.75; BILAG r = 0.61; ECLAM r = 0.65; all p < 0.0001). Correlations were somewhat lower with the blinded physician assessment (SLAM r = 0.42; SLEDAI r = 0.12; LAI r = 0.30; BILAG r = 0.28; ECLAM r = 0.32). The SLAM was the only index that was positively correlated with changes in the patient global assessment (r = 0.22; p < 0.0001). Sensitivity to change was greatest for the LAI (SRM = 0.74) and the ECLAM (SRM = 0.75) and smallest for the SLEDAI (SRM = 0.48) when the physician global assessment was used as the standard. Sensitivity to change was greatest for the SLAM (SRM = 0.61) and the BILAG (SRM = 0.57) and smallest for the SLEDAI (SRM = -0.01) when the patient global assessment was used as the standard.

Each index is a valid measure of SLE activity. The SLAM captures patients' assessments better than the other indices, perhaps because it assesses the patients' subjective complaints to a greater extent. Estimates of sensitivity to change varied with the standard used, but the SLEDAI was least sensitive to change. Larger studies are indicated to further compare the sensitivity to change of these indices.