Development and psychometric evaluation of a patient reported outcome measure for polymyalgia rheumatica

Background Polymyalgia rheumatica (PMR) causes pain, stiffness and disability in older adults. Measuring the impact of the condition from the patient’s perspective is vital to highquality research and patient-centred care, yet there are no validated patient reported outcome measures (PROMs) for PMR. The aims of this PhD are, i) to identify outcome measures and instruments used in clinical studies of PMR and evaluate the evidence supporting their use in the condition, and ii) to develop and evaluate a PMR-specific PROM. Methods Outcomes and instruments used in PMR research were systematically identified and categorised. Studies on their measurement properties were appraised. Two primary research studies were then undertaken: 1) 256 people with PMR completed a draft PROM providing data for item reduction, formation of dimension structure and scoring system development. 2) 179 people with PMR completed the PROM at two time points along with comparator questionnaires and anchor questions. Test-retest reliability, construct validity, and responsiveness were evaluated. Results The most frequent outcomes (and instruments) identified in the literature were: markers of systemic inflammation (ESR/CRP), pain (visual analogue scale), stiffness (duration) and physical function (elevation of upper limbs). No instruments had high-quality evidence to support their use in PMR. Results from the first study led to the development of a PROM, the PMR-impact scale (PMR-IS), comprising symptoms, function, emotional and psychological well-being and steroid side-effects domains. Construct validity and test-retest reliability were good for each domain of the PMR-IS. It was responsive to improvement in the condition but there was insufficient evidence to determine its ability to detect flares. Conclusions Current outcome measures used in PMR are not adequate. The PMR-IS provides a real opportunity to improve patient centred research and care, but further work is needed to more fully establish its responsiveness and interpretability parameters