Comparison of the Psychometric Properties of Three Fatigue Scales in Persian-Speaking Patients with Multiple Sclerosis.

Abstract

Fatigue is the most disabling symptom in patients with multiple sclerosis (MS). Although there is no standard tool to evaluate fatigue in clinical settings, the Fatigue Impact Scale (FIS), Fatigue Severity Scale (FSS), and Multidimensional Assessment of Fatigue (MAF) scale are popular instruments for this purpose. The aim of this study was to compare the psychometric properties of the Persian versions of these scales. One hundred thirty adult patients with MS and 60 controls participated in this study. They completed the scales on two occasions 3 days apart. Reproducibility and internal consistency were evaluated as intraclass correlation coefficients (ICCs) and Cronbach α. Convergent validity was assessed by evaluating the association of the fatigue scales with age, sex, Expanded Disability Status Scale (EDSS) score, disease duration, and sleep quality. Dimensionality was evaluated using confirmatory factor analysis. Acceptability and known-group validity were investigated. The effect size of each scale was computed. The ICC of all instruments was 0.99. Internal consistency was 0.97 for the MAF scale, 0.93 for FSS, and 0.83 for FIS. The instruments showed moderate-to-good correlations with Pittsburgh Sleep Quality Index, EDSS score, and disease duration. Acceptability was acceptable. The FIS had three dimensions, and the FSS and MAF scale were unidimensional. All scales were able to discriminate patients with MS from controls. The Persian version of the MAF scale seems to be the most suitable instrument to evaluate fatigue in patients with MS based on its time efficiency, effect size, and detailed data about various aspects of fatigue.