Development of a Patient-Reported Outcome Questionnaire to Evaluate Primary Mitochondrial Myopathy Symptoms: The Primary Mitochondrial Myopathy Symptom Assessment.

OBJECTIVES Primary mitochondrial myopathy (PMM) is a genetic condition characterized by life-limiting symptoms such as muscle weakness, fatigue, and pain. Because these symptoms are best reported by individuals with PMM, the objective of this qualitative research study was to develop a PMM-specific patient-reported outcome (PRO) questionnaire. METHOD Individuals with PMM were interviewed, identifying the most salient symptoms of PMM and assessing the resulting questionnaire's relevance and comprehensibility. RESULTS Developed based on patient interviews, the 10-item Primary Mitochondrial Myopathy Symptom Assessment assesses patients' symptom experiences at their worst in the last 24 hours. Individuals with PMM confirmed the concepts of the questionnaire as relevant and comprehensive to their symptom experiences and responded to the items consistently with developers' intentions. CONCLUSIONS The Primary Mitochondrial Myopathy Symptom Assessment is a content-valid PRO questionnaire with qualitative and quantitative support as a valuable tool to evaluate and monitor the day-to-day experience of PMM symptoms from the patient perspective.