Continuous long-term anti-TNF therapy does not lead to an increase in the rate of new bone formation over 8 years in patients with ankylosing spondylitis

Objective: Compare the radiographic progression of ankylosing spondylitis (AS) patients treated with infliximab (INF) versus historical controls (Herne cohort, HC) never treated with tumour necrosis factor (TNF)-blockers over 8 years. Methods: Patients were selected based on the availability of lateral cervical and lumbar radiographs at baseline (BL) and after 8 years. Radiographs were scored by two blinded readers using modified Stokes AS spinal score (mSASSS). Mixed linear models were applied to compare radiographic progression between cohorts after adjustment for baseline status. Results: Patients in INF (n=22) and HC (n=34) did not differ in the mSASSS status: 13.2±17.6 in INF versus 14.2±13.8 in HC (p=0.254). Both showed progression at 8 years: mean mSASSS 20.2±21.4 in INF and 25.9 ±17.8 in HC. After adjustment for baseline damage the mean mSASSS (SEM) at 8 years was 21.0 (1.4) in INF and 25.5 (1.1) HC (p=0.047). The mean mSASSS difference was similar in the groups between baseline and 4 years but was more pronounced in HC between 4 and 8 years (p=0.03 between groups). The mean number of syndesmophytes, although similar at baseline, differed significantly at 8 years: 1.0±0.6 new syndesmophytes/patient in INF versus 2.7±0.8 in HC (p=0.007). Adjustment for age, symptom duration, HLA-B27, Bath AS disease activity index and Bath AS function index at baseline had no influence. Conclusions: Despite limitations of patient numbers and retrospective study design, these data show increase in new bone formation in both patients treated with anti-TNF and those who did not. However, since there was even less bone formation in the INF treated group after 8 years, these data argue against a major role for the TNF-brake hypothesis.