Interestingly, 4 factors stood out in predicting treatment non-response in AS: older patients, HLA-B27 negative, normal baseline CRP, and higher baseline BASDAI.
The first 3 factors are "atypical" of AS; perhaps these are not truly AS patients after all! BASDAI is a purely subjective measure of disease activity, and is subject to being exaggerated by central pain sensitisation.
The development of anti-drug antibodies over time is an important cause of secondary treatment failure or loss of response.
In Ankylosing Spondylitis/Axial Spondyloarthritis Smoking Is Associated with a Dose Related Elevation in CRP, Worse Disease Activity and Worse Quality of Life over One Year
Smoking, obesity and dysbiosis are other factors to consider when patients fail to respond adequately to treatment.