Osteoporosis: a paradox in ankylosing spondylitis.

Ankylosing spondylitis is a chronic and severe inflammatory disease of the axial skeleton and the joints. Inflammation is associated with trabecular bone loss leading to osteoporosis but also with corcal new bone formation leading to progressive ankylosis of the spine and sacroiliac joints. This results in an apparent paradox of bone formation and loss taking place at sites closesly located to each other. Osteoporosis can be explained by the impact of inflammation of the bone remodeling cycle. In contrast, new bone formation has been linked to aberrant acvaon of bone morphogenec protein and Wnt signaling. In this commentary, we review recent data on this bone paradox and highlight recent advances including the effect of current drug therapies and the idenfication of new therapeutic targets.