FRI0433 Aspects of validity of the self-administered comorbidity questionnaire in patients with ankylosing spondylitis
Authors: C. Stolwijk, A. van Tubergen, S. Ramiro, I. Essers, M. Blaauw, D. van der Heijde, R. Landewé, F. van den Bosch, M. Dougados, A. Boonen
Journal: Annals of the Rheumatic Diseases (2013)

<h3>Background</h3> Comorbidities can importantly influence the results of clinical studies on health outcomes. The generic self-administered comorbidity questionnaire (SCQ) is a frequently used instrument to assess common comorbidities which might impact functioning but has never been validated for use in ankylosing spondylitis (AS). <h3>Objectives</h3> To evaluate aspects of validity of the SCQ in patients with AS. <h3>Methods</h3> The SCQ (range 0-45) asks about the presence, treatment and functional limitations of 12 common comorbidities and three possible other but not pre-specified medical problems. The SCQ, demographics and indices of disease activity (BASDAI, ASDAS-CRP); physical function (BASFI) and health-related quality of life measures (HRQoL; SF-36, ASQoL, EuroQoL-VAS, work status), were administered to 98 patients with AS who were followed in the Outcome in Ankylosing Spondylitis International Study (OASIS). The agreement between the SCQ-items and comorbidities retrieved from medical records was calculated. Truth was assessed by correlating the SCQ with the Charlson-index (predicting mortality) and Michaud/Wolfe-index (predicting health outcomes); by testing the hypothesis that a valid comorbidity index should correlate with age, function and overall HRQoL but not with disease activity; and by exploring the contribution of comorbidity to these outcomes while adjusting for clinical-demographic characteristics. Furthermore, a modified version of the SCQ (mSCQ), in which musculoskeletal conditions were removed was evaluated for the same aspects of truth. <h3>Results</h3> The median SCQ-score was 5 (range 0-19) and the median mSCQ-score was 2 (range 0-13). Frequently reported non-rheumatic comorbidities were hypertension (27.6%), inflammatory bowel disease (10.2%) and depression (9.2%). Agreement between self-report and medical records was moderate to perfect for all diseases included in the SCQ (kappa 0.47-1.00), except for stomach disease, depression, and osteoarthritis (kappa 0.14-0.15). The correlations of the SCQ with the Michaud/Wolfe index and the Charlson index were 0.39 and 0.24 respectively, and of the mSCQ with both indices 0.53 and 0.36 respectively. The SCQ correlated weakly with age (r=0.24) and disease activity (BASDAI r=0.27), and moderately with function (r=0.43), HRQoL (SF-36 physical r=-0.45; ASQoL r=0.43) and was associated with work status (OR 1.31, 95% CI 1.13-1.53). The mSCQ correlated weakly with age (r=0.28), moderately with function (r=0.41), HRQoL (SF-36 physical r=-0.41, ASQoL r=0.32) and with work status (OR 1.48, 95% CI 1.20-1.81), but not did not correlate with measures of disease activity. In multivariable analysis, both SCQ and mSCQ contributed independently to physical function, HRQoL and work disability, while the Michaud/Wolfe- and Charlson-index did not. <h3>Conclusions</h3> The SCQ is a promising instrument to determine comorbidities and to understand the impact on health outcomes in patients with AS. Excluding rheumatic conditions from the SCQ (mSCQ) improved truth. <h3>Disclosure of Interest</h3> None Declared