Bone formation in ankylosing spondylitis

Introduction Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disorder with unclear pathogenesis. Bone formation is a hallmark feature of AS, precise mechanisms of which are unknown. The aim of this review was to summarize the current knowledge regarding both clinical significance and pathogenesis of bone formation in AS. Materials and methods Articles, published in the medical literature and chapters in textbooks related to the discussed topic, were critically reviewed and relevant data were selected, collated and organized for the purpose of this manuscript. Results Conventional radiography is the most valuable classical tool for identification of structural changes in AS. The typical manifestations of bone formation in AS usually involve the axial skeleton, including spine, sacroiliac and hip joints, and, if properly recognized, have an important role in diagnosing, classifying and monitoring patients. Molecular pathways leading to bone formation in AS have not been elucidated sufficiently. Abnormally active signalling by wingless-type (wnt)-like and bone morphogenic protein (BMP)-mediated pathways have been suggested as major contributors to diseaserelated ossification in AS. The only medicines, shown currently to delay the process of bone formation in AS patients, are nonsteroidal anti-inflammatory drugs. Conclusion Better understanding and prediction of structural damage would help to improve and individualize management of patients suffering from AS.