Osteoporosis in Ankylosing Spondylitis

Osteoporosis (OP) is a frequent complication of ankylosing spondylitis (AS), even in early stages of the disease, and is associated with elevated levels of biochemical markers of bone turnover, proinflammatory cytokines, and acute-phase reactants. This suggests that systemic inflammatory mediators, such as interleukin-6 and tumor necrosis factor-α, may be involved. Various factors that conceivably work in conjunction with one another also cause bone loss in AS (eg, genetic polymorphisms of vitamin D, low levels of osteoprotegerin and sex steroid hormones, and impaired calcium and vitamin D absorption). Dual x-ray absorptiometry for assessing bone mineral density (BMD) has limitations in patients with AS because of unreliability of spinal measurements, particularly in advanced disease with new bone formation. Femoral neck BMD is reduced and correlates with increased risk of vertebral fractures. Hence, measurement of BMD at the femoral neck may provide the most accurate means of detecting osteopenia and OP and could assess fracture risk in AS patients. No guidelines are available for detection and treatment of OP in AS, and most patients are young men, who are less likely to be screened. The only evidence-based recommendation is that optimal control of disease activity in AS prevents bone loss. A recent study showed a beneficial effect of infliximab therapy on bone turnover markers and BMD in AS. Also, bisphosphonates may be useful in managing OP in AS.