Psychometric evaluation of the Polymyalgia Rheumatica-Impact Scale (PMR-IS); a new patient-reported outcome measure to assess quality of life in polymyalgia rheumatica

Problem

Polymyalgia rheumatica (PMR) causes pain, stiffness and disability in older adults. It usually has a sub-acute onset and responds rapidly to treatment with steroid medication, although the initial large improvement in health is typically followed by longer periods of lower level symptoms and episodes of relapse. Steroids themselves cause significant morbidity and adverse effects have to be balanced against PMR symptoms. Therefore, measuring the impact of PMR and its associated treatments from the patient’s perspective is of high importance, yet there are currently no validated outcome measures to support patient and clinician decision making. We have developed a patient-reported outcome measure (PROM) to assess PMR-related quality of life. The development process involved qualitative interviews, iterative item development and application of classical and modern measurement theory methods. The resultant PROM, the polymyalgia rheumatica-impact scale (PMR-IS), assesses key symptoms, function, psychological well-being and steroid side effects. Here we present assessment of the construct validity, test-retest reliability and responsiveness of the PMR-IS.

Approach

People diagnosed with PMR within the last 2 years were identified through GP practices (and one secondary care site) and invited to take part. Participants were asked to complete the PMR-IS, the modified Health Assessment Questionnaire (mHAQ) and the Short Form-36 (SF-36) at baseline and then the PMR-IS, the mHAQ and a series of anchor questions 2-6 weeks later. Questionnaire booklets were sent out via a secure mailing service (CFH Docmail) and returned directly to the research team. Construct validity will be assessed by testing hypotheses about relationships between domains of the PMR-IS and the other questionnaires. Test re-test reliability of each domain will be assessed in the sample of participants who report they ‘stayed the same’ between the two time points on that domain in the anchor questions.Responsiveness will be assessed by testing hypotheses about relationships between change in scores on the PMR-IS and change responses on the anchor questions.

Findings

Data collection is underway, and we will be able to present results of the analysis at the meeting.

Consequences

The PMR-IS is a newly developed PROM to assess PMR-related quality of life. Evaluation of its measurement properties is essential prior to being able to promote it as a reliable, valid, responsive measure for use in clinical research studies and in clinical practice. The availability of such a measure will enable the assessment of what truly matters to people with PMR to be incorporated into research into the condition and ultimately improve person-centred care for PMR.