Validation of the Russian version of the Fatigue Impact Scale and Fatigue Severity Scale in multiple sclerosis patients.

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Fatigue is a common complaint in patients with multiple sclerosis (MS), and its detection and monitoring are based on self-reported questionnaires. The objective of this study was to validate the Russian translation of the Fatigue Impact Scale (FIS) and the Fatigue Severity Scale (FSS) in MS patients and controls. We included 85 MS patients and 250 age-, sex-, and body mass index (BMI)-matched controls. We ascertained in all subjects levels of education, marital status, and comorbidities, such as sleepiness (using the Epworth Sleepiness Scale, ESS), anxiety and depression (using the Hospital Anxiety and Depression Scale, HADS). The expanded disability status scale (EDSS) reflected physical disability in MS. The Russian versions of the three FIS subscales (cognitive, physical, and psychosocial) and FSS had excellent internal consistencies (Cronbach's α coefficients 0.88-0.96), and good test-retest stability with intraclass coefficients between 0.78 and 0.89. Both convergent and discriminant validity of the Russian FIS and FSS appeared to be good, as expressed by strong inter-correlations between FIS subscales and FSS, and by absent associations between fatigue scales and BMI. Principal components analysis and scree plots indicated unidimensional structures of the physical and cognitive FIS subscales and FSS, but a multidimensional structure of the psychosocial subscale. We identified EDSS and anxiety scores as independent predictors of more severe fatigue in MS. The Russian FIS and FSS represent reliable and valid tools for efficient quantification and monitoring of fatigue severity and its clinical impact in MS. EDSS and anxiety are important contributors to fatigue severity in MS.