CONFIRMATORY PSYCHOMETRIC VALIDATION OF THE WESTERN ONTARIO MCMASTER UNIVERSITIES OSTEOARTHRITIS INVENTORY (WOMAC) IN ADULT X-LINKED HYPOPHOSPHATEMIA (XLH)
Author(s)
Skrinar A1, Theodore-Oklota C2, Bonner N3, Arbuckle R4, Williams A5, Nixon A6
1Ultragenyx Pharmaceutical Inc, Novato, CA, USA, 2Ultragenyx, Brisbane, CA, USA, 3Adelphi Values Ltd, Bollington, UK, 4Adelphi Values Ltd, Bollington, CHE, UK, 5Kyowa Kirin International, Newmarket, CAM, Great Britain, 6Chilli Consultancy Ltd, Salisbury, WIL, UK
OBJECTIVES: XLH is a rare genetic metabolic bone disorder with adult patients reporting pain, stiffness and reduced physical function. The WOMAC is used widely in osteoarthritis studies to measure these domains. This study sought to confirm an initial evaluation of the reliability, validity, responsiveness of the WOMAC in adult XLH patients, and to establish meaningful change thresholds. METHODS: Analyses were conducted using data (pooled across treatment groups) from a phase 3 multicenter, randomized, double-blind, placebo-controlled study to evaluate the efficacy and safety of burosumab in adults with XLH. RESULTS: Sample included 134 adult XLH patients, 64.9% female, mean age 40.0 (range 18-65 yrs). Floor effects (>20%) were marginally present in 5/24 items, no ceiling effects were present. Confirmatory factor analysis supported the 3-domain structure; item-scale correlations ranged between 0.59-0.80, and all items correlated highest with their intended scale. Internal consistency reliability was good for Physical Function (α=0.954), Pain (α=0.798) and Total Score (α=0.959), it was not tested for the 2-item Stiffness domain. Test-retest reliability was good when using the Patient Global Impression of Improvement (PGI-I) to define stability, although less favourable for Stiffness, likely influenced by the two-item structure. Known groups validity provided moderate to strong evidence that the WOMAC scores discriminate among patients who would be expected to differ. Correlations between WOMAC domains and external measures that were expected to correlate were moderate-strong for all domains and total score, but weaker for Stiffness. Overall, evidence for responsiveness of the WOMAC was good. Responder definitions for XLH patients were 8-10 point decrease for the Physical Function domain, 10-15 point decrease for the Stiffness domain, 11 point decrease for the Pain domain and 10 points for the total score. CONCLUSIONS: Results supported the use of the WOMAC to evaluate the effects of treatment interventions in clinical studies of XLH in adults.
Conference/Value in Health Info
2019-11, ISPOR Europe 2019, Copenhagen, Denmark
Code
PRO152
Topic
Clinical Outcomes, Methodological & Statistical Research, Patient-Centered Research
Topic Subcategory
Clinical Outcomes Assessment, Instrument Development, Validation, & Translation, PRO & Related Methods
Disease
Musculoskeletal Disorders, Rare and Orphan Diseases