Risk factors for functional limitations in patients with long-standing ankylosing spondylitis

Objective. To identify risk factors for functional limitations in patients with ankylosing spondylitis (AS) of at least 20 years' duration. Methods. Patients with AS for >= 20 years were enrolled in the cross-sectional component of the Prospective Study of Outcomes in AS. All patients had clinical evaluations and completed questionnaires on functional limitations and potential risk factors. Functional limitations were assessed using the Bath Ankylosing Spondylitis. Functional Index (BASFI; score range 0-100, higher scores indicate more limitations) and the Health Assessment Questionnaire for the Spondylarthropathies (HAQS). Risk factors included demographic characteristics, duration of AS, smoking status, number of comorbid medical conditions, recalled level of recreational activity in teens and twenties, occupational physical activity throughout life (rated 1 = little, 2 = moderate, 3 = heavy, and weighted by the number of years in each job), and history of AS in a first-degree relative. Results. The 326 patients (74% men) had a mean +/- SD age of 55.0 +/- 10.7 years, a mean duration of AS symptoms of 31.7 +/- 10.2 years, and a mean BASFI score of 40.7 +/- 25.6. BASFI scores increased with higher lifetime occupational physical activity (r = 0.31; P < 0.0001), the number of comorbid conditions (r = 0.25; P < 0.0001), and the duration of AS (r = 0.12; P = 0.04). BASFI scores were higher among current smokers compared with former/nonsmokers (55.5 versus 38.9; P = 0.0002), and among nonwhites compared with whites (49.9 versus 39.3; P = 0.02). In multivariable analyses, lifetime occupational physical activity, current smoking, education level, number of comorbid conditions, and family history were significantly associated with BASFI scores. The same risk factors were associated with the HAAS. Conclusion. Functional limitations in patients with AS for >= 20 years are greater among those with a history of more physically demanding jobs, more comorbid conditions, and among smokers, and are less severe among those with higher levels of education and a family history of AS.