Original ArticleDevelopment of a Patient-Reported Outcome Questionnaire to Evaluate Primary Mitochondrial Myopathy Symptoms: The Primary Mitochondrial Myopathy Symptom AssessmentGwaltney, Chad PhD*; Stokes, Jonathan MBA†; Aiudi, Anthony PharmD‡; Mazar, Iyar PhD†; Ollis, Sarah MPH†; Love, Emily BA†; Espensen, Ashlee MPH†; Shields, Alan L. PhD†Author Information *Gwaltney Consulting, Westerly, RI; †Adelphi Values, Boston, MA; and ‡Stealth BioTherapeutics Inc, Newton, MA. Reprints: Chad Gwaltney, 1 Bucks Trail, Westerly, RI 02891 (e-mail: [email protected]). Design, study conduct, and financial support for the study were provided by Stealth BioTherapeutics Inc. C. Gwaltney, J. Stokes, I. Mazar, S. Ollis, E. Love, A. Espensen, and A. Shields received consulting fees from Stealth BioTherapeutics, Inc. The Primary Mitochondrial Myopathy Symptom Assessment (PMMSA) reported on here is the sole property of Stealth BioTherapeutics Inc and reproduction, use, or modification to this tool must be done only with explicit written permission. For inquiries, please contact: +1 (617) 600-6888. Journal of Clinical Neuromuscular Disease: December 2020 - Volume 22 - Issue 2 - p 65-76 doi: 10.1097/CND.0000000000000303 Buy Metrics Abstract 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. Copyright © 2020 Wolters Kluwer Health, Inc. All rights reserved.