Background/Purpose:

The Ankylosing Spondylitis Quality of Life (ASQoL) is a readable and simple to complete questionnaire relating to health-related quality of life (HRQoL) in subjects with axial spondyloarthritis (axSpA). Although this tool has previously been used in various research settings over the last decade, the minimal clinically important difference (MCID) remains to be defined.

Methods:

All subjects seen at the Spondylitis Clinic of the Toronto Western Hospital between July 2003 and January 2018 with a diagnosis of 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 poorer HRQoL is associated with higher scores. The MCID for ASQoL was determined by anchor-based methods using two instruments to anchor the change on the ASQoL. The first anchor was the Health Transition Index (HTI) of the Short Form 36 (SF-36): “compared to one year ago, how would you rate your health in general now?”. The answers to this question at the yearly follow-up visit were incorporated in a 5-point Likert scale: “much worse” (-2), “somewhat worse” (-1), “about the same” (0), “somewhat better” (+1) or “much better” (+2). The second anchor was the change in the global self-rated health (GSRH) question of the SF-36 : “In general, would you say your health is […]”. The answers to this question are: “1- excellent”, “2- very good”, “3- good”, “4- fair” and “5- poor”. The level of change in GSRH between two consecutive visits was considered. A minimal change on the HTI was considered as anyone reporting better (+2 or +1) or worse (-2 or -1), and a minimal change on the GSRH was considered has those who had 1 level of improvement or worsening. The MCID for ASQoL was determined by plotting on receiver operating characteristic (ROC) curves the change in ASQoL that most accurately classified subjects based on optimal sensitivity/specificity ratio (improvement or worsening).

Results:

The study consisted of a total of 1328 subjects with longitudinal data cumulated over 5607 visits. Based on ROC curve analyses (image), the MCID for improvement is -2: this had a sensitivity of 40% and specificity of 84% anchored on the HTI, and sensitivity of 43% and specificity of 79% anchored on the GSRH. The MCID for worsening is 1, having a sensitivity/specificity of 40%/84% anchored on the HTI and 43%/79% anchored on the GSRH. Larger cut-off values for ASQoL resulted in a linear increase in the positive predictive value (PPV) up to thresholds of -5 for improvement (PPV=71% anchored on the HTI and PPV=55% anchored on the GSRH) and 5 for worsening (PPV=57% anchored on the HTI and PPV=53% anchored on the GSRH).

Conclusion:

This study gives values for MCID and further suggests that larger threshold values in ASQoL change may be applied to better classify subjects according to improvement or worsening in HRQoL. Defining cut-off values will enhance the utility of ASQoL in clinical and research settings.

« Back to 2018 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/establishing-the-minimal-clinically-important-difference-mcid-for-the-ankylosing-spondylitis-quality-of-life-questionnaire-asqol/