Background Previous studies showed no inhibition of spinal radiographic progression in patients with ankylosing spondylitis (AS) receiving TNF inhibitors for 2 years. There are few studies with more than 4 years of follow-up showing a possible reduction, but the results are under scientific debate.

Objectives To evaluate the course of spinal radiographic progression up to 8 years of follow-up in a large cohort of AS patients treated with TNF inhibitors.

Methods Consecutive patients from the Groningen Leeuwarden AS (GLAS) cohort who were treated with TNF inhibitors for 2 to 8 years were included. Baseline and biannual radiographs were randomized with radiographs of TNF naïve AS patients from a historical cohort and were scored in chronological time order by two independent readers according to the mSASSS. Longitudinal modeling of radiographic damage over time with generalized estimating equations (GEE) was used to investigate whether spinal radiographic progression followed a linear or non-linear course. The estimated progression rates per 2-year time interval were calculated based on the time model with the best fit for the data. Primary analysis was performed in patients with complete data over 4, 6, and 8 years of follow-up. Sensitivity analysis was performed after single linear imputation of radiographic data in case patients had missing data at one or more intermediate follow-up visits.

Results Of 188 included GLAS patients, 70% were male, 78% HLA-B27+, mean age was 42±11 years, median symptom duration 14 (IQR: 7–23) years, mean BASDAI 6.1±1.6, mean ASDAS 3.7±0.8, and mean mSASSS 9.8±15.3. Patients were exposed to TNF inhibitors during 97% (IQR: 83–100%) of their follow-up time. All baseline characteristics including mSASSS were similar between included and excluded patient, except for age (42 vs. 46 years).

During the first 4 years of follow-up, spinal radiographic progression followed a linear course (Table 1). A deflection of a linear course was found in patients with complete and imputed data over 6 and 8 years of follow-up. The estimated progression rates based on the time model with the best fit showed a reduction in progression over time (Table 1). The non-linear time model remained statistically significant after adjustment for patient characteristics including baseline radiographic damage (mSASSS and presence of syndesmophytes), gender, HLA-B27 status, age, symptom duration, smoking duration, BMI, disease activity, and NSAID use over time in both patients with complete en imputed data.

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Conclusions This observational cohort study in AS patients receiving TNF inhibitors showed a reduction in spinal radiographic progression after more than 4 years follow-up.

Acknowledgement The GLAS cohort was supported by an unrestricted grant from Pfizer. Pfizer had no role in the design, conduct, interpretation, or publication of this study.

Disclosure of Interest F. Maas: None declared, S. Arends Grant/research support from: Pfizer, E. Brouwer Grant/research support from: Pfizer, I. Essers: None declared, E. van der Veer: None declared, M. Efde: None declared, P. van Ooijen: None declared, R. Wolf: None declared, N. Veeger: None declared, H. Bootsma: None declared, F. Wink Consultant for: Abbvie, A. Spoorenberg Grant/research support from: Abbvie, Pfizer, UCB, Consultant for: Abbvie, Pfizer, MSD, UCB, Novartis