Predictors of longterm outcome in ankylosing spondylitis

Objective. To determine predictors of longterm outcome in ankylosing spondylitis (AS). Methods. Data were collected retrospectively on constitutional and environmental factors that may predict outcome in AS in 311 patients (252 men, 81%). Univariate statistics and multivariable linear regression analyses were used to identify factors correlated with disease outcome, which was defined in terms of radiological (Bath AS Radiology Index, BASRI) and functional status (Bath AS Functional Index, BASFI). Results. Disease duration. sex, and iritis are independently associated with BASRI and account for 23% (p < 0.001) of variation in radiological scores (BASRI-t), a measure that includes the hip joint in the score. Radiological hip involvement is significantly associated with higher scores of spinal radiological change (BASRI-s) (p < 0.001). Cigarette smoking, radiological status, and Bath AS Disease Activity Index score (BASDAI) are independently associated with and account for 50% of variability in functional status (p < 0.001). Conclusion. Much of the variability in disease severity in AS remains unexplained. All but one of the factors associated with outcome in this study are inherent. This suggests that genetic factors have a greater influence than environmental factors on radiological progression and disability in AS. It may, however, be possible to improve longterm functional outcome in AS by targeting high risk individuals early in the disease course with more aggressive management strategies and encouraging smoking cessation in all patients with AS.