Minimally important differences in the Mahler's Transition Dyspnoea Index in a large randomized controlled trial-results from the Scleroderma Lung Study

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 (means core = 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.