The Myotonic Dystrophy Health Index (MDHI) is a disease-specific, patient reported outcome measure for myotonic dystrophy type-1 (DM1). This instrument has been developed over the last five years using patient input from over 300 DM1 patients and guidance from the FDA.1 DM1 patients can complete our instrument in several minutes without difficulty. Each question in the instrument was selected based on its high relevance to the DM1 population, its ability to be consistently understood by patients, its reliability during test-retest evaluation, its content validity, its face validity, its construct validity, and its responsiveness in detecting both therapeutic change and differences between known groups.2
FDA guidelines were fully considered during every step of instrument development in order that the MDHI can be used as a potential drug labeling tool during upcoming DM1 therapeutic studies. 3 The instrument is capable of measuring the total health of a myotonic dystrophy patient as well as seventeen additional areas of relevant DM1 subhealth. These 17 areas were identified directly by patients and represent the most important symptoms related to their disease. These subscales directly measure a patient’s perception on their mobility, upper extremity function, ability to do activities, fatigue, pain, gastrointestinal function, vision, communication, sleep, emotional health, cognitive function, social satisfaction, social performance, myotonia, breathing, swallowing, and hearing.
Most recently, the construct and convergent validity of the MDHI has been confirmed during the COMFORT Study. 4 During this study, the MDHI and its subscales were shown to have widespread associations with other clinical assessments designed to measure similar concepts including 25 functional tests, six laboratory studies, and seven physician assessments while being well tolerated and accepted by patients.
The MDHI is currently being used as a patient relevant outcome measure in multiple academic, government, and pharmaceutic company studies worldwide including a FDA supported Phase II Therapeutic Treatment Trial for Myotonic Dystrophy Patients, a Study of Multiple Doses of ISIS-DMPKRx in Adults with Myotonic Dystrophy Type-1, multiple NIH longitudinal trials, a Myotonic Dystrophy Foundation study of pregnancy in myotonic dystrophy, and the European Optimistic Trial. It has been translated and culturally validated in other languages. Overall, the MDHI is optimally suited to detect small but clinically relevant changes in several key areas of myotonic dystrophy health over the course of a treatment trial.