Background/Purpose: Limited spinal mobility is a cardinal sign of ankylosing spondylitis (AS) and shows a close relationship with functional disability which leads to high individual socioeconomic consequences and lifetime costs. To measure the metrologic outcomes which may be critical in daily clinical practice, BASMI is used in conjunction with chest expansion which is for more accurate assessment of thoracic spinal mobility. ASDAS, a composite index score, was developed for assessment of disease activity and efficacy of treatment. Recently, ASDAS is known to be related with spinal mobility and radiographic spinal progression. In this study, we investigated whether early ASDAS changes is related with the longitudinal improvements of spinal mobility in patients treated with TNF-α blockers.

Methods: This was an observational study in 126 adult AS patients who were treated with TNF-α blockers up to 33 months. All outcome measures, including disease activity and metrologic outcomes, were performed at baseline and month 3, and then every six month up to month 33. Clinical efficacy was presented by ASAS and ASDAS response criteria, such as ASDAS major improvement (ASDAS-MI). Cumulative probability plots were used for association between ASDAS changes and metrologic improvements. Differences in BASMI₁₀ and chest expansion at any time point between responder and non-responder groups were examined with a mixed linear model.

Results: The BASMI₁₀ showed a rapid and significant improvement to month 3 (p<0.001), a further response to month 9 (p=0.003), and then maintained to month 33. The chest expansion considerably increased to month 3 (p=0.011) and then slowly improved up to month 33. ASDAS-CRP improved prominently at month 3 (p<0.001), a further significantly at months 9 (p<0.001) and mildly up to month 33. The cumulative probability plots, in which scatter plots of the individual 3-month ASDAS-CRP changes in cumulative order versus the 33-month BASMI₁₀ and chest expansion changes, demonstrated a significant tendency toward 33-month BASMI₁₀ improvements with 3-month ASDAS-CRP changes (r=0.383, p<0.001). The 33-month chest expansion changes showed a weak, but significant, tendency to increase with respect to 3-month ASDAS-CRP changes (r=-0.245, p=0.031). ASDAS-MI responders at month 3 had a significant improvement in 33-month BASMI₁₀ (p=0.011) and chest expansion changes (p=0.015), compared to non-responders, while baseline BASMI₁₀ and chest expansion were not significantly different. The mixed linear model revealed that a significant difference between two groups were detected in both BASMI₁₀ (p=0.0099) and chest expansion (p=0.0189). On the contrary, ASAS20 responders at month 3 did not show a significant difference in 33-month BASMI₁₀ and chest expansion improvements. On the analysis using a mixed linear model, BASMI₁₀ showed a significant difference between two groups (p=0.00375), while chest expansion scores were not different.

Conclusion: These results suggested that ASDAS-MI responsiveness at month 3, not ASAS20 responsiveness at month 3, may be related with an outstanding improvement in metrologic outcomes of long-term TNF-α blocker treatment in AS.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/early-achievement-of-asdas-major-improvement-in-patients-with-ankylosing-spondylitis-treated-with-tnf-%ce%b1-blockers-is-associated-with-a-prominent-longterm-improvement-in-metrologic-indices/