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We read the letter by our colleague W. Maksymowych, entitled ‘Evidence in support of the validity of the TNF brake hypothesis’ with great interest, which commented on our paper ‘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’.1 He argues that our interpretation of the results of our study is misleading in relation to the tumour necrosis factor (TNF) brake hypothesis proposed by him. Since there have been several versions of this hypothesis,2–4 we have decided not to go into much detail and semantics but rather discuss the recent progress in the field.
One of the major open questions related to the pathophysiology of AS is the nature of the link between inflammation and ankylosis. Several years ago we have reported that syndesmophyte formation after 2 years is more probable if, at baseline, spinal inflammatory lesions as detected by MRI using short-tau inversion recovery (STIR) sequences are present,5 and this finding was confirmed later.2
However, it was clear from the beginning that this could not be the only influencing factor, since the majority of syndesmophytes appeared to have grown from vertebral edges without any bone marrow oedema at baseline,2 ,5 and that finding was also confirmed later.6 In our most recent paper7 on imaging, results of …