The assessment of ankylosing spondylitis in clinical practice.

Ankylosing Spondylitis (AS) is a chronic inflammatory arthritis that predominantly affects the axial skeleton in adolescent patients causing spinal pain and stiffness. There is a marked delay, on average 8 years, between onset of disease symptoms and clinical diagnosis. The distinction between the symptoms of mechanical and inflammatory back pain remains one of the main contributing factors for the delay in diagnosis. Several classification criteria exist to aid the diagnosis of AS, but their accuracy is poor. The Ankylosing Spondylitis Assessment Study group (ASAS) has defined a core set of domains for clinical outcome measurement in AS in order to assess the disease process in individual patients and to identify those with rapidly progressive disease. New therapies, such as the tumor necrosis factor (TNF) inhibitors, have transformed the treatment paradigm in AS, especially for those patients with aggressive disease. Thus, the definition of both patient selection criteria for these agents and the development of clinical methods to assess response to therapy have become a priority. This Review focuses on measuring the degree of disease activity, function and damage in patients with AS in an ambulatory care setting, and the assessment of suitability of various outcome measures for monitoring response to treatment with TNF inhibitors.