Psoriatic arthritis quality of life instrument: an assessment of sensitivity and response to change.

Abstract

To assess responsiveness of the Psoriatic Arthritis Quality of Life tool (PsAQoL) and add further data regarding the construct validity of PsAQoL. Twenty-eight patients with PsA underwent clinical assessment over a period of 6 months after change of disease modifying therapy, usually to methotrexate. Measures of outcome included PsAQoL, Health Assessment Questionnaire (HAQ), and assessment of disease activity. PsAQoL revealed significant change at 3 and 6 months. Standardized response mean was large at 3 months and small at 6 months. There was strong correlation with other patient-derived measures such as the HAQ and Patient Global at all timepoints. Disease Activity Score-28 and Physician Global showed a relationship with PsAQoL at 3 and 6 months, while a tender joint count relationship was seen only at 6 months. The PsAQoL now has responsiveness data and a measure of construct validity to sit alongside previously demonstrated reliability data. Our study has compared the change characteristcs within a group of patients. The next step in the development will require a placebo controlled trial to test discrimination between patients undergoing active treatment or taking placebo.