Patient reported outcomes in ankylosing spondylitis: development and validation of a new questionnaire for functional impairment and quality of life assessment.

OBJECTIVES

To assess validity, reliability and sensitivity to change of a new questionnaire for assessment of functional disability and quality of life in ankylosing spondylitis (AS) patients.

METHODS

Using Rasch analysis and 71 questions item pool, content analysis and semi structured group discussion, the combined AS questionnaire (CASQ) was developed including: 10-item scale to assess functional impairment (CASQ-FI), and 10 items to assess quality of life (CASQ-QoL). Construct validity was assessed by correlating the score of the questionnaire to parameters of disease activity namely, the BAS-FI, BAS-DAI, BAS-G, BAS-Metrology Index, and the occupational status. In addition, the CASQ was compared to both HAQS and ASQoL. Sensitivity to change of the developed CASQ was also assessed.

RESULTS

The CASQ questionnaire for functional impairment (CASQ-FI: 10 items) and quality of life (CASQ-QoL: 10 items) showed acceptable validity as it correlated significantly with clinical parameters of disease activity: BAS-FI (CASQ-FI: r=0.85, CASQ-QoL: r=0.86), BAS-DAI (CASQ-FI: r=0.71, CASQ-QoL: r=0.87) and BAS-G (CASQ-FI: r=0.64, CASQ-QoL: r=0.79). Compared to HAQS and ASQoL, the CASQ-QoL was as well or better correlated with clinical and outcome measures. The CASQ was also reliable (Cronbach's alpha for CASQ-FI 0.958, and CASQ-QoL 0.966) and had no misfitting items. In addition, both CASQ questionnaires were sensitive to change (p<0.01)

CONCLUSIONS

The CASQ is a reliable and valid tool for assessment of functional impairment and quality of life in AS. The CASQ is well accepted by patients, sensitive to change, easy to administer and score. The CASQ-FI and CASQ-QoL questionnaires can either be used and scored separately to assess for functional disability as well as quality of life or in combination as tools to assess for both parameters.