Development and validation of a new instrument to measure health-related quality of life in patients with psoriatic arthritis: the VITACORA-19

Objective: To develop/validate an instrument to measure health-related quality of life (HRQoL) in patients with psoriatic arthritis (PsA), for use in clinical studies.

Methods: An item pool of 35 items was generated following standardized procedures. Item reduction was performed using clinimetric and psychometric approaches after administration to 66 patients with PsA. The resulting instrument, the VITACORA-19, consists of 19 items. Its validity content, internal consistency, test-retest reliability, known groups/convergent validity, and sensitivity to change were tested in a longitudinal and multicenter study conducted in 10 hospitals in Spain, with 323 patients who also completed the EuroQol 5-dimensional questionnaire (EQ-5D) and a health status transition item. There were 3 study groups: group A (n = 209, patients with PsA), group B (n = 71, patients with arthritis without psoriatic aspect, patients with arthrosis, and patients with dermatitis), and group C (n = 43, healthy controls).

Results: The questionnaire was considered easy/very easy to answer by 94.7% of the patients with PsA. The factorial analysis clearly identified only 1 factor. Cronbach's alpha coefficient and interclass correlation coefficients exceeded 0.90. Statistically significant differences (p < 0.001) were observed between groups: subjects from group C had better HRQoL, followed by group B, and finally group A had the worst HRQoL. The VITACORA-19 scores showed significant correlations (p < 0.001) to PsA disease activity, EQ-5D, and perceived health state, scoring the patients with better health state higher. The minimum important difference was established as an 8-point change in the global score.

Conclusion: The Spanish-developed VITACORA-19, designed to measure HRQoL in patients with PsA, has good validity, reliability, and sensitivity to change.