Rheumatology Advance Access published online on September 23, 2009
Rheumatology, doi:10.1093/rheumatology/kep284
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Minimally important differences in the Mahler's Transition Dyspnoea Index in a large randomized controlled trial—results from the Scleroderma Lung Study
1Department of Medicine, Division of Rheumatology, David Geffen School of Medicine, 2Department of Health Services, School of Public Health, 3Department of Medicine, Division of Biomathematics and 4Department of Medicine, Division of Pulmonary and Critical Care, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA, USA.
Correspondence to:
Dinesh Khanna, Department of Medicine, Division of Rheumatology, David Geffen School of Medicine, 1000 Veteran Avenue, Rm 32-59 Rehabilitation Building, Los Angeles, CA 90095, USA. E-mail: dkhanna{at}mednet.ucla.edu
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Abstract |
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Objective. Scleroderma Lung Study (SLS) showed that cyclophosphamide (CYC) was better than placebo (PLA) in preventing progression of forced vital capacity percentage (FVC%) predicted and dyspnoea at 12 months. Our objective was to assess minimally important difference (MID) for Mahler's Transition Dyspnoea Index (TDI) in SLS.
Methods. A total of 158 subjects participated in the SLS. Data from the two treatment groups were combined for this analysis. We used five patient-reported anchors from the short form (SF)-36 instrument to assess MID for TDI—SF-36 transition question and four questions from SF-36 pertaining to walking on a flat surface or climbing stairs. On the SF-36 transition question, patients who rated as a little better or a little worse were defined as the MID subgroup. For other questions, patients who reported improvement from ‘Limited a lot’ to ‘Limited a little’ and ‘Limited a little’ to ‘No limit’ and vice versa were defined as the MID subgroup.
Results. The MID estimates for the TDI improvement and worsening ranged from 1.05 to 2.16 (mean score = 1.5) U and from –0.61 to –2.55 (mean score = –1.5) U, respectively. Change in this group was larger than that of the no-change group (mean score = 0.38 U). Patients who achieved the MID for improvement at 12 months had a greater improvement in their FVC% predicted (3.6%) compared with those who did not (–3.3%; P < 0.001).
Conclusion. A change (improvement/worsening) of 1.5 U in the TDI is the MID for SSc-related interstitial lung disease (SSc-ILD). This can aid in interpreting clinically important changes in breathlessness in SSc-ILD.
KEY WORDS: Scleroderma, Lung disease, Minimally important differences, Minimal clinically important differences, Mahler's Dyspnoea Index, Scleroderma Lung Study
Submitted 19 May 2009;
revised version accepted 4 August 2009.
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