Validity and reliability of fatigue scale for motor and cognitive functions (FSMC) in an Iranian population of people with multiple sclerosis

Abstract

Introduction: Multiple sclerosis (MS) is a central nervous system disorder and is frequently associated with fatigue. The Fatigue Scale for Motor and Cognitive Functions (FSMC) is an instrument to assess both motor and cognitive dimensions of fatigue in MS. Methods: The study included 60 MS patients who completed the Persian version of the Modified Fatigue Impact Scale (MFIS) and a translated version of FSMC questionnaire. The FSMC was translated using standardized forward-backward translation, expert review, and patient feedback to ensure linguistic and conceptual validity. To evaluate test-retest reliability, participants completed the translated version of FSMC again after two weeks. Content validity was examined by a panel of eight experts. Results: Sixty individuals with a mean age of 36.36 +/- 9.7 years and an Expanded Disability Status Scale score of 3.00 +/- 2.0 were enrolled in this study. Fifty-one (85) of the participants were female. The Persian FSMC demonstrated strong content validity (Content Validity Index: 0.875-1.00; content validity ratio: 0.75-1.00). Internal consistency was excellent (Cronbach's alpha = 0.964). Test-retest reliability was strong for average scores (intraclass correlation coefficient (intraclass correlation coefficient (ICC) = 0.979), though fair to good for single measures (ICC = 0.540). Convergent validity was supported by strong correlations with MFIS scores (FSMC-total: r = 0.88; motor: r = 0.87; cognitive: r = 0.85; all p < .001). No floor/ceiling effects were observed. Conclusions: The Persian version of the FSMC is a valid and reliable instrument for assessing fatigue in Iranian patients with MS. With strong psychometric properties, it is well-suited for clinical and research use in Persian-speaking populations.