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

After pain and stiffness, one of the most important complaints of patients with ankylosing spondylitis (AS) is disability. The main aims of treatment are to control pain but also to improve function. Various methods of assessing function exist but are either not specific for the disease or have not been adequately validated. As a result of this deficiency we developed the Bath Ankylosing Spondylitis Functional Index (BASFI) as a new approach to defining and monitoring functional ability in patients with AS.

This self-assessment instrument was designed by a team of medical professionals in conjunction with patients, and consists of 8 specific questions regarding function in AS and 2 questions reflecting the patient's ability to cope with everyday life. Each question is answered on a 10 cm horizontal visual analog scale, the mean of which gives the BASFI score (0-10). The questionnaire was completed 257 times in total: once by 116 outpatients and by 47 inpatients on 3 occasions over a 3-week intensive physiotherapy course. In addition, the instrument was compared with the Dougados functional index.

Patients scores covered 95% of the BASFI range, giving a normal distribution of results. In contrast only 65% of the Dougados functional index scale was used. Furthermore, over the 3 week period of inpatient treatment, the BASFI revealed a significant improvement in function (20%, p = 0.004) while there was a less impressive change in the Dougados functional index (6%, p = 0.03). This demonstrates the superior sensitivity of the BASFI: Consistency was good for both indices (p < 0.001), as was the relationship between patient perception of function and function as assessed by an external observer (p < 0.001).

The BASFI satisfies the criteria required of a functional index: it is quick and easy to complete, is reliable and is sensitive to change across the whole spectrum of disease.