Fatigue in ankylosing spondylitis: Its prevalence and relationship to disease activity, sleep, and other factors

Objective. To assess the symptom of fatigue in patients with ankylosing spondylitis (AS) with regard to its prevalence and its relationship to disease activity and other factors. Methods. A self-administered questionnaire, including visual analog scales to assess fatigue, other components of disease activity, and functional ability (the Bathe AS Functional Index, BASFI) was sent to 350 patients with AS. Questionnaires were completed and returned by 295 patients (84% response rate). Statistical analyses were descriptive and predictive and included t test, chi-squared tests, and multiple regression. Results. Sixty-five percent of the patients (n = 192) described fatigue as a major symptom (F+ group) while 31% (n = 91; F- group) did not consider it to be important (4% noncommittal). Excluding fatigue, the mean of a disease activity composite score was significantly higher in the F+ group [5.26, standard deviation (SD) +/-2.33] than in the F- cohort (3.67, SD+/-2.09, p<0.001). The former group also had significantly worse scores on the functional index (BASFI mean 5.87, SD+/-2.42 vs 4.29, SD+/-2.46, p<0.001). Of the total, 55% had, on occasion, suffered fatigue without accompanying pain or stiffness. After controlling for other factors, pain (p<0.001), functional disability (BASFI, p<0.001) and stiffness (p<0.05) were significantly associated with level of fatigue. The F+ group reported more sleep disturbance, with 41% (compared to 26% of the F- group) waking more than 3 times a night (p=0.04). In addition, usual fatigue on waking was more common in the F+ group (71 vs 36%, p<0.001). Conclusion. (1) Fatigue is a major symptom in the majority of patients with AS, in particular those with more severe disease; (2) fatigue is more likely to occur with active disease but may also occur as a lone symptom; (3) those with severe fatigue function less well; and (4) the management of fatigue remains an enigma-exercise, for example, having only an equivocal effect.