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

Abstract EN

Background : pain, stiffness, functional impairment, range of motion and quality of life are the main conventional domains used in studies evaluating enclosing 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 to the conventional ones and to evaluate the sensitivity to change after non-steroidal anti-inflammatory drug (NSAID) therapy.

Methodology : 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 Enclosing 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).

Results : 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 R² 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).

Conclusions : 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.