Reconstructing the Rasch-Built Myotonic Dystrophy Type 1 Activity and Participation Scale.

Introduction: A previously published Rasch-built activity and participation scale specifically designed for patients with myotonic dystrophy type 1 (DM1) was criticized for having been constructed in a relatively small cohort of patients and containing items too broadly phrased for DM1 patients, thus hampering its clinical use.

Methods: We report the results of the reconstructed Rasch-built DM1 activity and participation scale for clinical use (DM1-ActivC) through Rasch analyses using an expanded questionnaire containing 146 more simply phrased activity and participation inquiries completed by 340 patients with DM1.

Results: Through stepwise investigation including data quality control, model fit, response category ordering, local dependency and item bias, we succeeded in reconstructing the DM1-ActivC consisting of 25 items that showed good Rasch model fit, including construct convergent validity, items' weights and persons' locations reliability, and unidimensionality.

Conclusion: The DM1-ActivC scale has been reconstructed and fulfills all modern clinimetric requirements. Its use is recommended in future longitudinal trials in patients with DM1 to determine its responsiveness.