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

A Cross-Sectional Study

Alice Horisberger; Delphine Courvoisier; Camillo Ribi

Disclosures

Arthritis Res Ther. 2019;21(80) 

In This Article

Discussion

To the best of our knowledge, ours is the first study that validates the FAS as a simple and reliable tool to assess fatigue in SLE. The FAS measures fatigue by means of 10 items including two reverse questions. This fatigue scale was previously shown to be useful and valid in the general population, in the working population, and in sarcoidosis patients. Fatigue is a prominent feature of SLE, a disease known for its wide range of symptoms. Brain fog is a common complaint in SLE patients, which refers to periods of impaired cognition[26] without any signs of neurolupus. Indeed, only a very few of the patients in this study had overt neurological disease. Fatigue is also a major complaint in other autoimmune diseases such as pSS. The thin line between cognitive dysfunction and depression in SLE and pSS makes fatigue assessment a particular challenge in this population. Our study shows that the FAS displays solid psychometric abilities, with an excellent internal consistency and test-retest reliability. Its convergent validity is supported by the good correlation with the VT-SF36. Concerning discriminant validity, it is revealed that fatigue and mental disorders such as depression are related but distinct constructs.

This cross-sectional study also shows that fatigue measured by FAS is significantly increased in both SLE and pSS patients compared to healthy controls. Several authors reported similar results for chronic inflammatory diseases, including SLE and pSS.[27,28] In previous studies, the prevalence of fatigue in SLE subjects varied from 76 to 90%.[3,29,30] By comparing FAS to the SF-36 subscales, we confirm the relationship between fatigue and various aspects of HRQoL, such as perceived mental health, emotional state, bodily pain, and social functioning in both SLE and pSS. We found that fatigue levels were higher in patients using psychiatric medication. Whether fatigue is the cause or the consequence of mental health issues and prescribed psychiatric medication in these patients remains to be established. SLE patients in our study differed from those with pSS in terms of disease duration from diagnosis, which was significantly shorter for pSS. On the other hand, pSS has a more insidious disease course than SLE. Diagnosis of pSS is often delayed by years and the duration of symptoms difficult to establish. This may explain why the time elapsed since pSS and SLE diagnosis in our study had no influence on the measured fatigue levels and reflects our clinical impression of long-standing fatigue in most patients suffering from these conditions. Moreover, we show that patients with active SLE have significantly more fatigue than healthy controls, whereas this difference is much less pronounced in those with inactive SLE. The association between fatigue and disease activity in SLE is controversial. Some authors reported a lack of association between disease activity and the Fatigue Severity Score.[30–32] Others, however, were able to show that fatigue increases with SLE activity, although to various degrees.[3,14,33] In the present study using two global scores (SELENA-SLEDAI and PGA) to ascertain SLE disease activity, we demonstrate a clear positive correlation with fatigue. Interestingly, patients with active SLE displayed a similar degree of fatigue than those with pSS. This observation amplifies the need for further investigation of immune factors that could contribute to fatigue in both active pSS and SLE. Recently, Petri et al. demonstrated a significant decrease in fatigue and disease activity in SLE patients treated with blisibimod, a selective inhibitor of B cell activating factor, in a phase 2b study. The authors found a weak correlation between disease activity and fatigue and concluded that this symptom appears to be closely related to immune dysfunction.[33,34] Others have found that the use of IL-6 blocking agents has a favorable impact on fatigue in SLE.[35] These findings could be explained by the impact of pro-inflammatory cytokines on the central nervous systemic with induction of illness behavior, expressed in symptoms such as fatigue and anhedonia.[36] The relief of fatigue after the use of various biological agents supports a relationship between fatigue and inflammation due to ongoing disease activity. We did not find any association of fatigue with traditional markers, such as auto-antibodies. This underlines the need for further studies to assess fatigue levels in relation to circulating cytokines and novel biomarkers in autoimmune disease.

Our study has some limitations. We did not assess additional factors potentially contributing to fatigue, such as sleep disorders, depression, and physical activity. Our study is cross-sectional and does not allow the determination of the sensitivity to change. Longitudinal studies with FAS are needed to assess variations in fatigue, and its causes and its impact on health-related quality of life and working capacity both in SLE and pSS.

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