Bone turnover and predictors of response in ankylosing spondylitis. Results from the GLAS study

PhD ceremony: Ms. S. Arends, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Bone turnover and predictors of response in ankylosing spondylitis. Results from the GLAS study

Promotor(s): prof. C.G.M. Kallenberg

Faculty: Medical Sciences

Ankylosing spondylitis (AS) is a chronic rheumatic disease predominantly affecting the axial skeleton and sacroiliac joints. The disease is characterized by inflammation in combination with excessive bone formation (resulting in ankylosis of the spine) and bone loss (resulting in vertebral fractures). This thesis is based on data from the Groningen Leeuwarden AS study, a prospective observational cohort study. Since November 2004, approximately 400 AS outpatients of the MCL and UMCG were included in the study. The general research goals were to obtain more knowledge on the bone metabolism in AS and to evaluate the effect of tumor necrosis factor-alpha (TNF-α) blocking therapy in a large group of AS patients.

In clinical practice, continuation of TNF-α blocking therapy is mainly based on subjective measures such as the BASDAI (questionnaire about fatigue, pain, and stiffness) and the opinion of the patient and the physician. Our results show that the decrease in sCTX (marker of bone resorption) and the improvement in ASDAS (composite score of patient-reported measures and acute phase reactants) during the first 3 months of treatment, were predictive for continuation of TNF-α blocking therapy. These (partly) objective measures therefore seem useful for the clinical evaluation of TNF-α blocking therapy. Furthermore, our study demonstrates that bone turnover markers (BTM) can be useful to identify bone loss in AS, especially in patients with advanced disease. BTM can easily be measured in the blood of patients at different time points with relatively low costs.