Selecting patients with ankylosing spondylitis for TNF inhibitor therapy: comparison of ASDAS and BASDAI eligibility criteria.

OBJECTIVE: To compare Ankylosing Spondylitis Disease Activity Score (ASDAS) ≥2.1 with BASDAI >4 as an eligibility criterion for initiation of TNF inhibitor (TNFi) treatment in AS, and to investigate if ASDAS performs satisfactorily in patients without elevated CRP or without peripheral joint swelling.

METHODS: Two hundred and eighty-nine patients starting their first TNFi were identified from a longitudinal observational study (NOR-DMARD) and grouped according to the fulfilment of ASDAS and BASDAI TNFi eligibility criteria. The 3-month responses were compared across several response measures. Patients were also grouped according to CRP level and the presence or absence of swollen joints, and responses were compared.

RESULTS: The majority of patients (n = 212) fulfilled both eligibility criteria, and this group had the best response. Very few patients (n = 4) fulfilled only the BASDAI criterion. Patients fulfilling only the ASDAS criterion (n = 48) had a reasonable response. Patients with an elevated vs not elevated CRP at baseline had better responses according to all response measures, but patients without elevated CRP also responded. We also observed trends towards better responses in patients with vs without peripheral joint swelling.

CONCLUSION: More patients were eligible for TNFi using the ASDAS than the BASDAI eligibility criterion (n = 260 vs n = 216). Fulfilment of both criteria gave the greatest likelihood of improvement, but the patients who only fulfilled the ASDAS criterion also improved. ASDAS was found to be applicable also in subgroups without elevated CRP and without peripheral joint swelling.