Ankylosing Spondylitis and Antiphospholipid Antibodies

The main objective is to evaluate the prevalence of anti-phospholipid antibodies (APLA) in patients with ankylosing spondylitis (AS). The secondary objectives are: (1) To determine whether the presence of these antibodies is symptomatic (thrombosis or not); (2) Identify a possible relationship between the presence of APLA and a particular form of SA (axial or peripheral); (3) To determine whether the presence of APLA is more frequent in patients receiving anti-tumor necrosis factor (TNF) alpha therapy.