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FRI0208 Ankylosing spondylitis quality of life: defining minimal clinically important change
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  1. N. Richard1,2,
  2. N. Haroon1,2,
  3. G.A. Tomlinson1,2,
  4. I. Sari1,2,
  5. Z. Touma1,2,
  6. R.D. Inman1,2
  1. 1University Health Network
  2. 2University of Toronto, Toronto, Canada

Abstract

Background The Ankylosing Spondylitis Quality of Life (ASQoL) is a readable and simple to complete questionnaire relating to health-related quality of life (HRQoL) in ankylosing spondylitis (AS) and it has been shown to be a reliable and valid outcome measure[.1 Despite that this tool was used in various research settings over the last decade, the Minimal Clinically Important Difference (MCID) remains to be defined.

Objectives Our objective is to define the MCID of ASQoL in subjects with axial spondyloarthritis(axSpA).

Methods All subjects seen at the Spondylitis Clinic of the Toronto Western Hospital between July 2003 and January 2018 with a diagnosis of axSpA [AS or non-radiographic axSpA (nr-axSpA)] were included in this study. The ASQoL comprises 18 questions, and answers are dichotomized into yes/no. The weighted score for each item is 1 and poor HRQoL is associated with higher scores. The Medical Outcomes Study Short Form-36 (SF-36) is an instrument to assess for health status. Subjects completed ASQoL and SF-36 at the same time during yearly visits in the clinic. To determine MCID for ASQoL the SF-36 question 2 (SF-36 Q2; “compared to one year ago, how would you rate your health in general now?”) was used as an anchor measure. The answer to this question was incorporated in a 5 point Likert scale: “much worse”(−2 points), “somewhat worse”(−1 point), “about the same”(0 point), “somewhat better”(+1 point), “much better”(+2 points). An important change on the anchor was determined as +2 for improvement and −2 for worsening on the Likert scale. MCID was determined based on the optimal threshold that discriminated between change and no change (improvement or worsening) using receiver operating characteristic (ROC) curve analyses.

Results A total of 1328 subjects were seen during the follow-up period. Of these, 66.2% were male, 75.3% were Caucasian, 61.8% had college or more education and the proportion AS/nr-axSpA was 84%/16%. At baseline, the mean age was 38.7 years and the mean disease duration was 14.9 years. On follow-up visit, patients who reported “much worse”, “somewhat worse”, “about the same”, “somewhat better” and “much better” had a mean change in ASQoL of respectively 3.85, 1.30,–0.24, −0.94 and −3.45 (table 1). Differences between mean change in ASQoL were statistically significant(p<0.02). The area under the ROC curve was 0.72 (95% CI 0.66–0.79) for subjects who worsened and 0.69 (95% CI 0.66–0.72) for those who improved. The ROC curve analyses showed that for thresholds of −2.5 and −3.5 points in deterioration there was a sensitivity/specificity of 0.536/0.841 and 0.474/0.890, respectively. Similarly, cut-offs of +2.5 and+3.5 points in improvement showed a sensitivity/specificity of 0.464/0.825 and 0.389/0.883, respectively.

Conclusions We identified the MCID for ASQoL; a 3 points change for both improvement and worsening. Defining MCID will enhance the clinical utility of ASQoL in the management of patients with axSpA.

Reference [1] Doward LC, Spoorenberg A, Cook SA, et al. Development of the ASQoL: A quality of life instrument specific to ankylosing spondylitis. Ann Rheum Dis2003;62:20–6.

Disclosure of Interest None declared

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