Active-NDM: Development of a patient-reported outcome questionnaire to measure the impact of non-dystrophic myotonia on activity of daily living

Background: There is a considerable challenge in managing non-dystrophic myotonias (NDM), due to the lack of gold-standard outcome measures to assess NDM burden on activities of daily living and quality of life from the patient's perspective. Objective: In this study, we aim to develop and validate a specific NDM patient-reported outcome (PRO) questionnaire. Methods: The Active-NDM questionnaire was developed through a modified 2-round Delphi procedure integrating feedback from stakeholders and a systematic literature review, with input from 11 national clinical experts. The questionnaire was validated in a pilot study of 10 patients with NDM. Both clinical experts and patients assessed questions for pertinence/relevance and clarity. We excluded questions that were not considered pertinent/relevant, and reformulated any judged to be poorly formulated, by >80% of the experts/patients. We also excluded questions with <80% reproducibility during the pilot study. Results: Based on feedback from experts and findings of the systematic literature review, we identified 130 questions, of which 100 were unduplicated. During the Delphi process, we removed 66 questions due to lack of pertinence and/or relevance. In the pilot study, patients with NDM evaluated the resulting 34-questions for pertinence, clarity, and reproducibility. Subsequently we removed 9 questions that did not achieve the required level of reproducibility. Conclusion: We developed the Active-NDM questionnaire, composed by 25 questions, figuring as a new NDM-specific measure to determine the impact of the disease on patients’ activities of daily living and quality of life. Active-NDM could be a valuable tool in the management of patients with NDM. These findings should be interpreted as preliminary. Larger-scale validation studies are warranted to confirm the tool's psychometric properties and generalizability. ClinicalTrials.gov identifier: NCT06136416