Background/Purpose: TNF-α inhibitor therapy is recommended by ASAS/EULAR guidelines for ankylosing spondylitis (AS) patients with moderate-to-high disease activity despite inadequate response to NSAIDs  in addition to education and exercise.  The purpose of this study is to evaluate factors associated with anti-TNF-α use over a 13 year period in a longitudinal cohort of AS patients enrolled between 2003 and 2013.

Methods: A prospective cohort study of 607 AS patients meeting modified New York criteria were followed for at least 2 years from 5 sites. Patients underwent a comprehensive standardize clinical evaluation and completed questionnaires assessing their disease activity and functional impairment by the BASDAI and BASFI respectively.  Demographic, social, and psychological variables were collected. Current medication lists as well as ESR and CRP levels were determined at each visit. Multivariable longitudinal analyses using mixed effect logistic regression models were conducted to assess the clinical, demographic, and lab features associated with anti TNF-α usage accounting for correlation of repeated measures over time.  

Results: The patients were 73% male and 82% of white race, with a mean age of 42.7 years (SD = 13.8), mean disease duration of 18 years (SD = 13.2) and average length of follow up of 4.96 years.  TNF-α inhibitor therapy was used in 45% of patients at baseline visit, with increased rate of usage over the 13 year study period (p=0.0001).  Multivariable longitudinal associations between independent variables and anti TNF-α usage for the 607 AS patients (Table 1) demonstrated significant associations with greater disease activity in the previous week (by patient global assessment) and higher baseline BASRI scores.  On the other hand, patients with disease duration of more than 20 years, those with elevated CRP, or those using NSAIDs or prednisone were less likely to be using anti-TNFα therapy.  Male gender, BASFI score, BASDAI score, Center for Epidemiologic Studies Depression (CES-D) scale score, greater pain severity (on a visual analog scale), acetaminophen and tramadol use were not  significantly associated with usage of TNF-α inhibitors.

Conclusion: This large, prospective, longitudinal cohort study shows multiple subjective and objective factors associated with anti TNF-α therapy. Patients with longstanding disease, laboratory evidence of inflammation and using anti-inflammatory medications were less likely to be using anti-TNF therapy. Those with more severe radiographic changes at baseline and higher patient global assessment of disease activity were more likely to be using TNF-α inhibitors.

Table 1 Multivariable Associations of Selected Variables on Longitudinal anti TNF-α use (N = 607)