Assessment of fatigue in the management of patients with ankylosing spondylitis

Background. Pain, stiffness, functional impairment, range of motion and quality of life are the main conventional domains used in studies evaluating ankylosing spondylitis (AS). However, fatigue has been reported as the major complaint of AS patients. Objectives. To evaluate fatigue as a potential independent domain in comparison with the 'conventional' ones and to evaluate the sensitivity to change after nonsteroidal anti-inflammatory drug (NSAID) therapy. Methods. Patients were classified as having painful AS (modified New York criteria). The following variables were recorded at baseline and after 6 weeks of therapy (either placebo or NSAIDs): pain (VAS), function (Bath Ankylosing Spondylitis Functional Index), patient's global assessment (VAS), inflammation (night pain), morning stiffness, metrology (Schober test, finger-to-floor) and fatigue using 0-100 VAS scale. Analysis consisted of (i) the prevalence of fatigue (VAS value of at least 50 mm), (ii) the independence of the information evaluated using a regression model, and (iii) the sensitivity to change, by calculating the standardized response mean (mean change/S.D. change) (SRM) between placebo and NSAID group. Results. Fatigue was considered important in 401 patients (out of 639: 63%). The information provided by the variables 'pain', 'function' and 'global assessment' explained only 44% of the variability of the variable 'fatigue' (similar analyses considering 'pain' on the one hand and 'function' on the other hand as the dependent variables showed an R 2 value of 34 and 60%, respectively). The NSAID treatment effect (SRM) was higher for the variables 'pain' and 'function' (0.76 and 0.71, respectively) than for the variable 'fatigue' (0.34). Conclusion. This study strongly suggests that fatigue should be considered as an independent domain to be systematically evaluated in AS patients and that conventional therapy such as NSAIDs have a lower effect on this domain than on pain or functional impairment.