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


Group Characteristics

Seventy-three patients with SLE, 23 patients with pSS, and 23 healthy volunteers were included (Table 1). There was no statistical difference in demographic features between groups. SLE subjects were predominantly women (89%), of Caucasian origin (77%) and had a median age of 43 years at assessment. Median disease duration from diagnosis was 7 (3–15) years in patients with SLE compared to 1 (0–2) in those with pSS (p < 0.001). Patients with SLE were more frequently treated with systemic corticosteroids and immunosuppressant drugs compared to those with pSS. Among SLE patients treated with immunosuppressants, four had received cyclophosphamide in the month preceding the study. Within the SLE group, 23 (32%) had active disease (SELENA-SLEDAI ≥ 4 and PGA ≥ 1). Table 2 compares the characteristics of SLE patients according to their disease activity.

Psychometric Analysis of FAS

The internal consistency of the FAS was measured at 0.93 (Cronbach's alpha coefficient), and none of the items would have improved the internal consistency if removed. Principal component analysis favored a one-component solution, confirmed by visual inspection of the scree plot (Figure 1). The factor analysis of FAS items extracted a unique factor explaining 64% of the variance with the items loading between 0.68 (item 3) and 0.88 (item 5).

Figure 1.

Scree plot of the Fatigue Assessment Scale (FAS) and its items

Of the 73 SLE subjects, 30 (41%) had a test-retest assessment. Seven patients were excluded because of a self-reported significant event between the first and the second FAS assessment. There was no difference in age, sex, ethnicity, and disease activity between the whole SLE sample and the test-retest subjects (data not shown). The test-retest correlation was good with an ICC of 0.90 (95%CI 0.80–0.95, p < 0.001) for a 2-week interval. The FAS correlated strongly with the VT-SF36 subscale (rs = 0.85, p < 0.001). The FAS correlation with the MH-SF36 was rs = 0.65 (p < 0.001). The PCA on the combined pool of the FAS and the MH-SF36 items favored a two-component solution (eigenvalue factor I, 8.4; factor II, 1.9; percentage explained variance, 69%). One statement of the ten FAS items (FAS-7) loaded higher on the mental health scale. All other items loaded higher on the fatigue factor. All items of the MH-SF36 loaded higher on the mental health factor (Table 3). These results were similar using a larger sample including SLE, pSS, and HV (data not shown) except for the item FAS-7 showing a higher loading on the fatigue factor (0.48) than on the mental factor (0.42).

Comparison of Fatigue Levels Between Groups

The FAS score was significantly increased in both SLE and pSS compared to healthy subjects. Median (IQR) FAS was 23 (17–32) in SLE, 27 (20–34) in pSS, and 16 (14–18) in HV (p = 0.001). These fatigue findings were confirmed using the VT-SF36 subscale (median VT score [IQR] = 45[23–58] in SLE, 35[15–50] in pSS, and 70[50–75] in HV, p = 0.001). There was a good correlation between the FAS and the VT-SF36 score among all groups of participants (Table 4). There was a lesser but significant correlation between FAS and the other subscales of the SF36 in both SLE and pSS. In contrast, HV showed modest to the non-significant correlation between FAS and SF-36 subscales other than VT. In the three groups of participants, no correlation was found between the total FAS score and demographic features such as age, sex, ethnicity, educational status, and BMI (data not shown). Tobacco use was weakly associated with a higher degree of fatigue in the pSS group (p = 0.024). The use of psychiatric medication was associated with higher fatigue levels in both SLE (p = 0.002) and pSS (p = 0.047) patients, but not in HV.

Association of Fatigue and Disease Activity in SLE Patients

The median (IQR) FAS score was 31 (20–36) in patients with active SLE, compared to 22 (15–27) in those with inactive disease (p = 0.005). In healthy volunteers, the FAS score was slightly lower than in patients with inactive SLE (p = 0.05). In contrast, patients with active disease presented with a significant higher level of fatigue than HV (p < 0.001) (Figure 2). No association was found between fatigue and other clinical parameters such as the time elapsed from diagnosis to assessment, number of ACR criteria fulfilled at inclusion, presence of renal involvement at any time during disease course, presence of auto-antibodies (anti-dsDNA and anti-SSA/Ro) at study visit, and damage accrual (SDI score). There was no difference in levels of fatigue between SLE patients with or without a history of renal disease (median [IQR] FAS was 24[17–32] and 23,[16–31] respectively). Fatigue was higher in the patients treated with corticosteroids (r = 0.27, p = 0.022). There was no difference when comparing fatigue with the use of other DMARDs. In a linear regression model, after adjusting for corticosteroids and psychiatric medication use at visit, active disease remained significantly associated with fatigue so that FAS increased on average by 6.2 points (95%CI 2.2–10.3, p = 0.003) for each additional point in disease activity.

Figure 2.

Fatigue Assessment Scale (FAS) scores in 73 patients with systemic lupus erythematosus (SLE) according to disease activity and controls with primary Sjogren's syndrome or in good health. SLE systemic lupus erythematosus, FAS Fatigue Assessment Scales (ranges from 10 – no fatigue to 50 – extreme fatigue), pSS primary Sjogren's syndrome, Healthy healthy volunteers. Plots represent the individual values (diamonds), the median score, and the IQR for each group. *p < 0.05; **< 0.001