A new approach to defining functional ability in ankylosing spondylitis: the development of the Bath ankylosing spondylitis functional index

The clinical assessment of disease activity in patients with AS is often not easy. A few functional indices have now been developed for longitudinal follow-up of AS patients, and for monitoring their response to therapy. The most widely used measures of functional capacity in AS is the Bath ankylosing spondylitis functional index (BASFI) (score 0-10). Disease activity has been assessed by using a self-administered composite index called the Bath ankylosing spondylitis disease activity index (BASDAI) that consists of an evaluation on a visual analogue scale (from 0-10) focusing on axial pain, peripheral joint pain, fatigue/tiredness, enthesitis, and morning stiffness). BASDAI has been found to be a valid and appropriate composite to define disease activity in AS.