Myotonic Dystrophy Health Index: Initial evaluation of a disease-specific outcome measure

Introduction: In preparation for clinical trials we examine the validity, reliability, and patient understanding of the Myotonic Dystrophy Health Index (MDHI). Methods: Initially we partnered with 278 myotonic dystrophy type-1 (DM1) patients and identified the most relevant questions for the MDHI. Next, we used factor analysis, patient interviews, and test-retest reliability assessments to refine and evaluate the instrument. Lastly, we determined the capability of the MDHI to differentiate between known groups of DM1 participants. Results: Questions in the final MDHI represent 17 areas of DM1 health. The internal consistency was acceptable in all subscales. The MDHI had a high test-retest reliability (ICC = 0.95) and differentiated between DM1 patient groups with different disease severities. Conclusions: Initial evaluation of the MDHI provides evidence that it is valid and reliable as an outcome measure for assessing patient-reported health. These results suggest that important aspects of DM1 health may be measured effectively using the MDHI.