The Fatigue Assessment Scale as a Simple and Reliable Tool in Systemic Lupus Erythematosus

A Cross-Sectional Study

Alice Horisberger; Delphine Courvoisier; Camillo Ribi


Arthritis Res Ther. 2019;21(80) 

In This Article


Study Population

Participants were aged ≥ 18 years old and attended the Centre Hospitalier Universitaire Vaudois (CHUV) in Lausanne between June 2015 and July 2016. All were included in the Swiss Systemic Lupus Erythematosus Cohort Study (SSCS).[16,17] All SLE patients fulfilled the revised American College of Rheumatology (ACR) criteria and/or the Systemic Lupus International Collaborating Clinics (SLICC) criteria.[18,19] Control groups consisted of patients with primary Sjogren syndrome (pSS) meeting the 2002 American-European Classification Criteria[20] and age- and gender-matched healthy volunteers (HV). Patients with completed FAS and SF-36 forms were retained for the cross-sectional study. Patients with pSS were asked to participate in the cohort study during their regular clinical follow-up. The HV were recruited by public notice in the CHUV and were evaluated medically to confirm the good health and absence of autoimmune disease or immunomodulatory treatment. The protocol was approved by the Canton Vaud ethical committee. All participants gave their written informed consent, and the study was carried out in compliance with the Helsinki Declaration.

Data collection and instruments. Data on patient's age, sex, ethnicity, educational status, tobacco use, body mass index (BMI), disease duration since diagnosis, activity and damage, and treatment modalities were collected during the medical visit. Disease activity in SLE was assessed by the SLE Disease Activity Index with the Safety of Estrogens in Lupus Erythematosus National Assessment modification (SELENA-SLEDAI).[21] This score is based on 24 clinical and biological items, which reflect disease activity within the past month. Disease activity was also evaluated using the Physician's Global Assessment score (PGA) with a 4-point-Likert-scale ranging from 0 (inactive) to 3 (very active disease).[21] Patients with a SELENA-SLEDAI ≥ 4 and a PGA ≥ 1 were considered to have active disease.[22] Damage was assessed in SLE with the SLICC/ACR Damage Index (SDI).[23] Disease-modifying treatment (DMARD) at study visit and in the 4 weeks before was classified into three groups: systemic glucocorticoids, antimalarials, and immunosuppressants. Data on health-related quality of life (HRQoL) and fatigue were assessed with the Short Form 36 (SF36) and the FAS in all participants. The SF36 is a widely used health survey form measuring 8 dimensions of QoL; each of them ranges from 0 to 100 with lower scores reflecting poorer health. The SF-36 vitality subscale (VT-SF36) is used for convergent validity of fatigue questionnaires.[24] The mental health subscale of the SF-36 (MH-SF36) was used for the discriminant validity. The FAS comprises 10 questions with answers varying from never to always on a 5-point-scale. The total FAS score ranges from 10 to 50, increasing proportionally to fatigue. Both questionnaires were completed by participants during the study visit. A sample of 30 SLE patients was asked to complete the FAS 2 weeks after the first assessment. These patients were reminded by text messages to complete and send back the questionnaire after 2 weeks with a pre-stamped envelope. Eligibility for this test-retest study was a completed form, and the absence of important intercurring events reported by the patient that would influence the state of fatigue during the test-retest period. FAS, SF-36, demographical data, and clinical data were collected in the two control groups of pSS patients and HV.

Statistical procedure. Descriptive statistics were presented as absolute count and percent for qualitative data and as median and interquartile range (IQR) for quantitative. Difference between groups and correlations were evaluated using non-parametric tests. The psychometric properties of the FAS were evaluated using the following methods. Cronbach's alpha was calculated to measure the reliability of the tool by looking at inter-item consistency. This measure is generally considered satisfactory if the alpha value is above 0.7 for group-level analysis but a value above 0.9 is desirable for individual patients in clinical application.[25] A factor analysis was performed using the principal component analysis (PCA) based on Kaiser criteria (eigenvalue > 1) and visual inspection of the scree plot. A PCA was used with the FAS and the MH-SF36 in order to examine the divergent validity (construct validity) of the FAS. Factor analysis extraction was presented with an oblimin rotation. A coefficient factor above 0.3 was considered significant. As there were slightly less than 5 (4.87) patients per item for this measure, we confirmed the results on a larger sample using SLE, pSS, and HV. The convergent validity was examined with a Spearman's rho correlation between FAS and VT-SF36. The test-retest reliability was measured using intraclass correlations (ICC). A linear regression model was used for multivariable analysis, with total FAS score as dependent variable and disease activity and corticoid use as independent variables. P values < 0.05 were considered significant. All statistics were performed on IBM SPSS statistics 24 (IBM Corp Armonk, NY) and GraphPad Prism 7 (GraphPad Software, La Jolla, CA, USA).