Feasibility and face validity of outcome measures for use in future studies of Polymyalgia Rheumatica (PMR): An OMERACT Study

Objective: The aim of this study was to survey participants with PMR to evaluate the face validity, acceptability and domain match of proposed candidate outcome measures.

Methods: A structured, online, anonymous survey was disseminated by patient support groups via their networks and online forums. The candidate outcome measures comprised: 1. visual analogue scale (VAS), numerical rating score (NRS) to assess pain; 2. VAS, NRS and duration to assess stiffness; 3. the modified Health Assessment Questionnaire (mHAQ) and Health Assessment Questionnaire Disability Index (HAQ-DI) to assess physical function; 4. C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR) to assess inflammation. Free text answers were analysed using descriptive thematic analysis to explore respondents' views of the candidate instruments.

Results: Seventy-eight people with PMR from six countries (UK, France, USA, Canada, Australia and New Zealand) participated in the survey. Most respondents agreed candidate instruments were acceptable or “good to go”. Free text analysis identified five themes which participants felt were inadequately covered by the proposed instruments. These related to: (i) the variability, context and location of pain, (ii) the variability of stiffness, (iii) fatigue, (iv) disability, and (v) the correlation of inflammatory marker levels and severity of symptoms, sometimes reflecting disease activity and other times not.

Conclusion: Participants reported additional aspects of their experience which are not covered by the proposed instruments particularly for the experience of stiffness and impact of fatigue. New patient-reported outcome measures are required to increase the relevance of results from clinical trials to patients with PMR.