Validity and reliability characteristics of the Silhouettes Fatigue Scale in measuring multiple sclerosis-related fatigue in Turkish-speaking adults

Background The purpose of this study is to investigate the reliability and validity as well as the clinical utility of the Silhouettes Fatigue Scale (SFS), a single-item visual scale to assess fatigue, in adult patients with multiple sclerosis (MS). Methods The study included 61 MS patients and 73 matched healthy controls. Demographic data and disease-related variables of all participants were recorded. Then, the SFS, Visual Analogue Scale (VAS)-fatigue, Fatigue Impact Scale (FIS), Fatigue Severity Scale (FSS), and Beck Depression Inventory (BDI) were applied. SFS, VAS-fatigue, and FSS were repeated after one week. Reliability was evaluated with the intra-class correlation coefficient (ICC) and Bland-Altman analysis. Validity was tested by comparison of healthy controls and patients with MS and correlations with other scales. Accuracy and clinical utility were also evaluated. Results SFS scores were 4.49 +/- 3.11 (mean +/- SD) in MS patients and 1.40 +/- 1.44 in healthy controls (p < .001). The ICC for SFS was 0.946. The mean difference between test-retest measurements of SFS was -0.04651 (-95% CI, -0.4815-0.38848), and there was no systemic bias. SFS scores were not correlated with the expanded disability status scale, whereas they were poorly correlated with BDI. Correlations ranging from poor to good were calculated between the SFS and other fatigue-related scales. The optimum cut-off score of the SFS scale was four, with a sensitivity of 0.72 and a specificity of 0.84. Conclusion This study demonstrated that the SFS is a reliable, responsive, and valid scale with acceptable sensitivity and specificity to assess and quantify clinically significant fatigue in MS patients. These findings as well as the brief and understandable nature of the SFS were encouraging that this scale has good clinical utility.