What do we miss? ASAS non-responders on anti-TNF therapy show improvement in performance-based physical function

Objective: A prospective study was conducted in order to establish whether AS patients, who are defined as non-responders after 3 months of anti-TNF therapy, show improvement on performance-based tests of physical functioning. Methods: At baseline and 3 months after the start of anti-TNF therapy, AS patients completed seven performance-based tests of physical functioning, questionnaires on self-reported physical functioning (BASFI) and disease activity (BASDAI), and a pain and a global patient assessment. The concordance between ≥20% intra-individual improvement on the performance-based test of physical functioning and (i) response to anti-TNF therapy [Assessment of SpondyloArthritis International Society 20% (ASAS20) response] and (ii) ≥20% intra-individual improvement on self-reported physical functioning (BASFI) was assessed. Results: One hundred AS patients were included, of which 82 patients completed all tests at both time points. After 3 months of anti-TNF therapy, 27 (32.9%) patients were categorized as non-responders according to the ASAS20 response criteria. Improvement in performance-based physical functioning was seen in 13 of the 27 non-responders (48.1%) (i.e. n = 13/82 = 15.9% of the total group). Furthermore, 30 (36.6%) patients showed no improvement on self-reported physical functioning (BASFI). However, 17 of the 30 (56.7%) patients did improve on the performance-based tests of physical functioning (i.e. n = 17/82 = 20.7% of the total group).Conclusion: After 3 months of anti-TNF therapy, performance-based tests of physical functioning showed improvement in 48.1% of the ASAS20 non-responders. With these performance-based tests, new information on outcome after anti-TNF therapy can be generated. Using performance-based tests alongside the BASFI could have additional value in the evaluation of outcomes for patients receiving anti-TNF therapy.