Predictors of response to anti-TNF therapy in ankylosing spondylitis: results from the British Society for Rheumatology Biologics Register

OBJECTIVE Few data exist on the use of anti-TNF drugs for AS during routine clinical use in the UK. This report describes an improvement in Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Bath Ankylosing Spondylitis Functional Index (BASFI) after 6 months of therapy in 261 patients enrolled in a national prospective observational register. METHODS The British Society for Rheumatology Biologics Register (BSRBR) recruited patients starting anti-TNF therapy for AS between 2002 and 2006. Multivariable linear regression models were used to estimate the predictors of absolute improvement in BASDAI and BASFI at 6 months. Covariates included age, gender, disease duration, baseline BASDAI and BASFI, presence of raised inflammatory markers (defined as twice the upper limit of normal) and DMARD therapy. RESULTS The cohort was young (median age 43 years) and 82% were males. Median baseline BASDAI was 7.6 and BASFI 7.9. At 6 months, the mean improvements in BASDAI and BASFI were 3.6 and 2.6 U, respectively; 52% reached a BASDAI50. Patients with raised inflammatory markers at the start of therapy had a 0.9-U (95% CI 0.2, 1.5) better improvement in BASDAI compared with those without. Lesser responses were seen in those with higher baseline BASFI scores. Women had a 1.1-U (95% CI 0.3, 2.0) greater improvement in BASFI at 6 months, as did those who were receiving concurrent DMARD therapy [0.9 U (95% CI 0.2, 1.7)]. CONCLUSIONS The majority of patients receiving anti-TNF therapy for AS during routine care demonstrated an improvement in disease activity. Raised inflammatory markers at the start of therapy predicted a greater improvement in BASDAI, identifying a group of patients who may be more responsive to anti-TNF therapies, although the results were not confined to this group.