Background/Purpose: Although never formally studied, rheumatologists feel that patients with ankylosing spondylitis (AS) tend to adjust to their disease. Response shift is one of the theories to demonstrate that adaptation takes place and makes use of the ‘then test’. A ‘then test’ asks patients to re-rate their past health in a situation where change in health occurred. This theory states that patients with a treatment response would re-rate their former health as worse as initially thought, and that the magnitude of treatment response is associated with a larger gap between the initial and retrospective assessment of health. The aim of the present study was to understand whether patients with AS adapt to their disease, using the ‘then test’, in patients in whom infliximab (INF) was started. It was hypothesized responders to therapy would re-rate retrospectively their initial health as worse.

Methods: Data were used from 103 European patients who participated in the AS Study for the Evaluation of Recombinant INF Therapy (ASSERT) and continued in the European AS INF Cohort (EASIC). The Bath AS Global Score (BAS-G) last week was used to assess patient global well-being. A BAS-G ‘then test’ was integrated in EASIC, and asked patients to re-rate their initial well-being (i.e. before the start of INF in ASSERT). Treatment response between ASSERT and EASIC was assessed with the Assessment of SpondyloArthritis International Society 20 (ASAS20) response criteria. The baseline BAS-G of ASSERT and retrospective BAS-G of ASSERT were compared using paired t-test. Limits of agreement were calculated. A linear regression analysis was performed to identify whether response influenced the difference between the initial and retrospective BAS-G of ASSERT (i.e. gap) after adjusting for other covariates.  

Results: 86 Patients contributed to the current analyses (mean age 39.6 years (SD 10.6); mean disease duration 9.7 years (SD 8.1), and 68/96 (79.1%) patients had an ASAS20 response). At baseline, the BAS-G in ASSERT was 7.0 (SD 1.6), and patients retrospectively re-rated their BAS-G, using the ‘then test’, at 7.2 (SD 2.3), revealing a non-significant and non-relevant gap of 0.2 (SD 2.7) (p=0.45). Limits of agreements show that the gap varied between -5.1 and 5.5. In a multivariable model, the difference between the baseline BAS-G of ASSERT and retrospective BAS-G of ASSERT was irrespective of treatment response, and was only associated with the baseline BAS-G of ASSERT (p<0.01) and the BASDAI (p=0.02) before the start of INF.  

Conclusion: Patients with AS were able to retrospectively judge their well-being, even if substantial time relapsed between the start of the treatment and this retrospective assessment, and irrespective of treatment response. In this setting, the ‘then test’ could not prove adaptation by response shift in AS.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/patients-with-ankylosing-spondylitis-do-not-adapt-to-their-disease-evidence-from-the-then-test-in-patients-treated-with-tnf-inhibitors/