Bone mass in ankylosing spondylitis

Specific spine ossifications or syndesmophytes are considered to be a hallm ark of ankylosing spondylitis (AS) and to reflect a process of bone formati on. Conversely, AS patients may develop osteoporosis (OP), as suggested by radiographic studies, an increased frequency of the vertebral fracture rate and reduced bone mass. Dual energy X-ray absorptiometry measurements have clearly demonstrated decreased bone mineral density (BMD) at both the lumba r spine and femoral neck. However; for patients with advanced spinal change s, ossifications may yield normal or increased values for the lumbar spine BMD. Assessment of biochemical markers of bone metabolism have shown that b oth bone formation and resorption are involved, with enhanced urinary excre tion of markers of collagen breakdown inpatients with active disease and ra ised inflammatory parameters, and changes in the levels of some bone growth factors. The pathophysiology of this osteoporosis in AS mainly involves di sease activity and, very likely, inflammatory cytokines. Finally, vertebral fractures complicating this bone loss contribute to spine deformity in pat ients with AS.