Pathology: bone
Axial spondyloarthritis is associated with different types of skeletal damage. Inflammation at the affected sites is linked with both loss of trabecular bone and new bone formation on the cortical side, potentially leading to joint or spine ankylosis. Both aspects of the disease can result in a significant burden for the patient. Bone loss is directly linked to proinflammatory cytokines and activation of osteoclasts. Control of inflammation is therefore the best strategy to prevent loss of bone. The nature of the new bone formation process is less defined. A prominent role for developmental signalling pathways has been proposed. Current therapies have limited or no impact on this process. However, emerging data suggest that early control of disease activity may be part of a window of opportunity to prevent structural damage, as biomechanical factors and instability following inflammation may also play a role.