To the Editor:
We read with great interest the editorial1 by David A. Isenberg related to our article, “Development and Assessment of Users’ Satisfaction with the Systemic Lupus Erythematosus Disease Activity Index 2000 Responder Index-50 Website”2 (S2K RI-50).
Dr. Isenberg states that a drawback of the S2K RI-50 is that it does not identify patients whose clinical features are worse. However, outcome measures in clinical trials in systemic lupus erythematosus (SLE) measure improvement from baseline, or flares over the course of the study from baseline. Both of these are well identified by Systemic Lupus Erythematosus Disease Activity Index (SLEDAI-2K) and S2K RI-50. Flares can certainly be ascertained by SLEDAI criteria (increase by 4 or more)3 and the S2K RI-50 identified an improvement that is less than complete resolution4. Thus the index has the necessary features to be a primary outcome measure in SLE drug trials. Unlike BILAG, it is simple, intuitive, and gives actual metrics for improvement, not lettered categories such as A, B, C, etc.
The S2K RI-50 Website, www.s2k-ri-50.com, is currently being used to prepare clinicians to use the S2K RI-50 in clinical trials and research settings2.