Objective: To estimate minimally important differences (MIDs) in scores for the modified Rodnan Skin Score (mRSS) and Health Assessment Questionnaire—Disability Index (HAQ-DI) in a clinical trial on diffuse systemic sclerosis (SSc).
Participants and methods: 134 people participated in a 2-year, double-blind, randomised clinical trial comparing efficacy of low-dose and high-dose d-penicillamine in diffuse SSc. At 6, 12, 18 and 24 months, the investigator was asked to rate the change in the patient’s health since entering the study: markedly worsened, moderately worsened, slightly worsened, unchanged, slightly improved, moderately improved or markedly improved. Patients who were rated as slightly improved were defined as the minimally changed subgroup and compared with patients rated as moderately or markedly improved.
Results: The MID estimates for the mRSS improvement ranged from 3.2 to 5.3 (0.40–0.66 effect size) and for the HAQ-DI from 0.10 to 0.14 (0.15–0.21 effect size). Patients who were rated to improve more than slightly were found to improve by 6.9–14.2 (0.86–1.77 effect size) on the mRSS and 0.21–0.55 (0.32–0.83 effect size) on the HAQ-DI score.
Conclusion: MID estimates are provided for improvement in the mRSS and HAQ-DI scores, which can help in interpreting clinical trials on patients with SSc and be used for sample size calculation for future clinical trials on diffuse SSc.
- d-Pen, d-penicillamine
- HAQ-DI, Health Assessment Questionnaire—Disability Index
- HRQOL, health-related quality of life
- MID, minimally important difference
- mRSS, modified Rodnan Skin Score
- SSc, systemic sclerosis
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↵* Current address: Amgen, Thousand Oaks, California, USA
Published Online First 15 March 2006
Funding: This study was supported in part by grants from the Scleroderma Federation; United Scleroderma Foundation; FDA Orphan Drug Program; Arthritis Foundation; CRC grant numbers M01RR00865 and M01RR00827; WH Conzen Endowment in Clinical Pharmacology of the Schering-Plough Foundation; and bequests from the estates of Winifred Krause, Morris Goldsmith and Takako Ito. DK was supported by the Arthritis and Scleroderma Foundations (Physician Scientist Development Award), the Scleroderma Foundation (New Investigator Award), a National Institutes of Health BIRCWH Award (grant number HD051953) and a grant from the Scleroderma Clinical Trial Consortium. RDH was supported in part by the UCLA/DREW Project EXPORT, National Institutes of Health, National Center on Minority Health & Health Disparities (P20-MD00148-01), the UCLA Center for Health Improvement in Minority Elders/Resource Centers for Minority Aging Research, National Institutes of Health, and National Institute of Aging (AG-02-004).
Competing interests: None declared.
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