Validity and reliability of the Patient-Reported Arthralgia Inventory: validation of a newly-developed survey instrument to measure arthralgia

BACKGROUND There is a need for a survey instrument to measure arthralgia (joint pain) that has been psychometrically validated in the context of existing reference instruments. We developed the 16-item Patient-Reported Arthralgia Inventory (PRAI) to measure arthralgia severity in 16 joints, in the context of a longitudinal cohort study to assess aromatase inhibitor-associated arthralgia in breast cancer survivors and arthralgia in postmenopausal women without breast cancer. We sought to evaluate the reliability and validity of the PRAI instrument in these populations, as well as to examine the relationship of patient-reported morning stiffness and arthralgia. METHODS We administered the PRAI on paper in 294 women (94 initiating aromatase inhibitor therapy and 200 postmenopausal women without breast cancer) at weeks 0, 2, 4, 6, 8, 12, 16, and 52, as well as once in 36 women who had taken but were no longer taking aromatase inhibitor therapy. RESULTS Cronbach's alpha was 0.9 for internal consistency of the PRAI. Intraclass correlation coefficients of test-retest reliability were in the range of 0.87-0.96 over repeated PRAI administrations; arthralgia severity was higher in the non-cancer group at baseline than at subsequent assessments. Women with joint comorbidities tended to have higher PRAI scores than those without (estimated difference in mean scores: -0.3, 95% confidence interval [CI] -0.5, -0.2; P<0.001). The PRAI was highly correlated with the Functional Assessment of Cancer Therapy-Endocrine Subscale item "I have pain in my joints" (reference instrument; Spearman r range: 0.76-0.82). Greater arthralgia severity on the PRAI was also related to decreased physical function (r=-0.47, 95% CI -0.55, -0.37; P<0.001), higher pain interference (r=0.65, 95% CI 0.57-0.72; P<0.001), less active performance status (estimated difference in location (-0.6, 95% CI -0.9, -0.4; P<0.001), and increased morning stiffness duration (r=0.62, 95% CI 0.54-0.69; P<0.0001). CONCLUSION We conclude that the psychometric properties of the PRAI are satisfactory for measuring arthralgia severity.