Exercise habits and C-reactive protein may predict development of spinal immobility in patients with ankylosing spondylitis.

To assess predictors for spinal immobility in a long-term clinical study of patients with AS, data from annual clinical measurements of spinal mobility in 54 patients (41 men, mean of age at end of follow-up 54.7 years) with ankylosing spondylitis were co-analysed with data regarding lifestyle factors as well as laboratory measurements from a previous cross-sectional study. Spinal immobility was graded on the basis of recently published age-, sex- and length-specific reference intervals. Exercise habits and high-sensitivity C-reactive protein (hsCRP) were independently associated with the development of subnormal spinal immobility (p = 0.019 and p = 0.021). In multiple regression models, approximately 25% of the spinal immobility could be attributed to disease duration (p ≤ 0.011), levels of hsCRP (p ≤ 0.004) and exercise in leisure time (p ≤ 0.019). The mean concentration of hsCRP was 4.2 mg/L (range 0.2-8.4 mg/L) in the study cohort. Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), erythrocyte sedimentation rate (ESR) and physical activity at work were not associated with spinal immobility. The results indicate that exercise habits may have an impact in preventing the development of spinal immobility in AS independently of disease duration and inflammation. This corresponds well with the accumulated knowledge from long-term clinical experience among rheumatologists, health professionals and patients. Consequently, exercise should remain an important part of the non-pharmacological treatment and self-care for patients with AS. Furthermore, modest inflammatory activity, measured as a slightly elevated hsCRP concentration, appears to affect subsequent spinal immobility in AS.