Measuring fatigue in patients with multiple sclerosis: reproducibility, responsiveness and concurrent validity of three Dutch self-report questionnaires.

PURPOSE: To determine the reproducibility, responsiveness and concurrent validity of Dutch versions of the Fatigue Severity Scale (FSS), Modified Fatigue Impact Scale (MFIS), and Checklist Individual Strength (CIS20R) in patients with multiple sclerosis (MS).
METHOD: Forthy-three ambulatory patients with MS (mean age 48.7 years; SD 7 years; 30 women; median Expanded Disability Status Scale score 3.5) completed the questionnaires twice within 1 week. The Intraclass Correlation Coefficients (ICCs), Bland and Altman analysis, the smallest detectable change (SDC) and the minimal detectable change (MDC) were calculated. Concurrent validity was determined by Pearson's correlation coefficients.
RESULTS: ICCs ranged from 0.76 (FSS), to 0.85 (MFIS) to 0.81 (CIS20R). Bland and Altman analysis showed no significant systematic differences between assessments. MDCs were 20.7% (FSS), 19.23% (MFIS), and 17.7% (CIS20R). Pearson correlation coefficients were r = 0.66 (FSS-MFIS), r = 0.54 (MFIS-CIS20R) and r = 0.42 (CIS20R-FSS).
CONCLUSION: Despite good test-retest reliability of FSS, MFIS and the CIS20R, the present study shows that fatigue questionnaires are not very responsive for change in patients with MS. This finding suggests that future trials should monitor profiles of fatigue by repeated measurements rather than pre-post assessments alone. The moderate associations suggest that the three questionnaires largely measure different aspects of perceived fatigue.