Introduction: Fatigue is a symptom of systemic lupus erythematosus (SLE), which has a substantial effect on the patients' quality of life and is a parameter that is difficult to quantify. The Fatigue Severity Scale (FSS) is a validated and reliable tool for quantifying fatigue. However, no Danish translation has yet been developed or validated. The aim of this study was to translate the FSS from English into Danish and subsequently to test and describe its validity and reliability in Danish SLE patients.
Material and methods: The FSS was translated from English into Danish and then back-translated. The translation agreed upon by medical professionals was tested for construct validity in an unselected group of SLE patients. The final version was tested for content validity, internal consistency and test-retest reliability in a second unselected group of SLE patients using the Danish version of the Short-Form Health Survey (SF-36). All patients included were outpatients with SLE of low to moderate disease activity, and low to moderate organ damage.
Results: Correlations were found between the Danish FSS and the main component scores of the SF-36. We found a high Cronbach's alpha as well as acceptable results of the intraclass correlation coefficient and the Bland-Altman plot.
Conclusion: The Danish FSS translation is a valid and reliable measure of fatigue in the Danish SLE patients included in this study.
Funding: Anne Voss reported a grant from The Danish Rheumatism Association (R33-A1836) and grants from The A.P. Møller Foundation for the Advancement of Medical Science and finally grants from the Region of South Denmark during the conduct of the study.
Trial registration: not relevant.