Factors associated with body function and disability in patients with ankylosing spondylitis: a cross-sectional study.

OBJECTIVE

To determine for patients with ankylosing spondylitis (AS) which factors are associated with disability and restricted body function.

METHODS

In 1538 patients with AS, occiput-to-wall distance, chest expansion, cervical rotation, finger-floor distance, and modified Schober test were measured cross-sectionally, and for each measure the patient's respective percentile was calculated. The mean of the 5 percentiles was summarized in the mobility restriction score (MRS). In addition, patients answered questions on disease progression and completed the Bath AS Functional Index (BASFI) questionnaire. All data were coded into 40 variables, used as independent variables in multiple regression analyses to identify factors associated with BASFI and MRS.

RESULTS

Finger-to-floor distance (beta positive, +), cervical rotation (-), time since first AS symptoms (-), age (+), height loss (+), maximum height (-), delay in diagnosis (+), hip replacement (+), regular practice of sports (-), chest expansion (-), sex (worse BASFI in females), exposure to cold and dampness (+), and regular participation in AS group physical exercises (+) were significantly associated with worse BASFI. Significantly associated factors for worse MRS were height loss (+), sex (higher MRS in males), active inflammation of the cervical region (+), age (+), maximum height (-), active inflammation of the hip region (+), involvement of shoulders (+), time since first AS symptoms (+), urethritis (-), regular practice of sports (-), involvement of feet (-), and hip replacement (+). The models explain 47% of the variance observed for both the BASFI and MRS.

CONCLUSION

The amount of variance explained for both BASFI and MRS is rather high. The results apply primarily to groups of patients, but are insufficient to guide clinical decisions in individual patients. These findings contribute to our understanding of factors influencing disability and restriction in body function in AS.