Assessment of fatigue in ankylosing spondylitis patients: clinical and self-reported measures

ABSTRACT

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. To evaluate fatigue as a potential independent domain in comparison to the conventional ones and to evaluate the sensitivity to change after non-steroidal anti-inflammatory drug [NSAID] therapy. Twenty patients were selected as having painful AS [modified New York criteria 1984]. The following variables were recorded at baseline and after six weeks of NSAID therapy 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 the prevalence of fatigue [VAS value of at least 50mm] and the sensitivity to change, by calculating the standardized response mean [mean change / S.D. change] [SRM] between before and after NSAID therapy. Fatigue was considered important in 14 patients [out of 20 70%]. The information provided by 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 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 "fatigue" [0.34]. 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 fatigue than on pain or functional impairment