Marie Kierkegaard, Émilie Petitclerc, Luc J. Hébert, Jean Mathieu, Cynthia Gagnon
Function Area Occupational therapy & Physiotherapy, Karolinska University Hospital, SE-171 76 Stockholm, Sweden. E-mail: Marie.Kierkegaard@ki.se, marie.kierkegaard@sll.se
DOI: 10.2340/16501977-2304

Objective: To assess changes and responsiveness in outcome measures of mobility, balance, muscle strength and manual dexterity in adults with myotonic dystrophy type 1.
Design: A 9-year longitudinal study conducted with 113 patients.
Methods: The responsiveness of the Timed Up and Go test, Berg Balance Scale, quantitative muscle testing, grip and pinch-grip strength, and Purdue Pegboard Test was assessed using criterion and construct approaches. Patient-reported perceived changes (worse/stable) in balance, walking, lower-limb weakness, stair-climbing and hand weakness were used as criteria. Predefined hypotheses about expected area under the receiver operating characteristic curves (criterion approach) and correlations between relative changes (construct approach) were explored.
Results: The direction and magnitude of median changes in outcome measures corresponded with patient-reported changes. Median changes in the Timed Up and Go test, grip strength, pinch-grip strength and Purdue Pegboard Test did not, in general, exceed known measurement errors. Most criterion (72%) and construct (70%) approach hypotheses were supported. Promising responsiveness was found for outcome measures of mobility, balance and muscle strength. Grip strength and manual dexterity measures showed poorer responsiveness.
Conclusion: The performance-based outcome measures captured changes over the 9-year period and responsiveness was promising. Knowledge of measurement errors is needed to interpret the meaning of these longitudinal changes.

How well do measures of mobility, balance, muscle strength and manual dexterity capture changes in myotonic dystrophy type 1 (DM1) patients’ physical performance?
Mobility, balance, muscle strength and manual dexterity were assessed in 113 patients with DM1 nine years apart. Patients also reported whether they perceived themselves being stable or changed to the worse regarding balance, walking, lower-limb weakness, stair-climbing and hand weakness. We found that the outcome measures chosen were able to well capture changes, and that measured changes also corresponded with patient-reported changes. Although measures of grip strength and manual dexterity seemed less sensitive, the results indicate promising ability of the used outcome measures to properly, over time, identify patients that remained physically stable and the ones that did not.