Further evidence for the reliability and validity of the Fatigue and Daytime Sleepiness Scale

Background: Myotonic dystrophy type 1 (DM1) is an inherited neuromuscular disease causing, among other symptoms, fatigue and excessive daytime sleepiness, which are frequently undifferentiated by patients and/or clinicians. The Fatigue and Daytime Sleepiness Scale (FDSS) has been devised to measure these two overlapping symptoms as a single clinical entity. Objective: To further examine the reliability and the construct validity of the FDSS in patients with DM1. Methods: The scale was administered to 48 DM1 patients on two occasions at a 2 week-interval. Intra-rater reliability and internal consistency were established by calculating the intraclass correlation coefficient (ICC) and Cronbach's alpha, respectively. Construct validity was assessed by using the known-group method. More precisely, the mean FDSS score of patients with and without subjective complaints of fatigue and/or sleepiness was compared. Results: The FDSS showed good intra-rater reliability (ICC = 0.83) and acceptable internal consistency (Cronbach's alpha = 0.6). Also, the FDSS was able to distinguish between patients who had fatigue and sleepiness complaints from those who did not (mean FDSS score of 10.6 vs 8.0,p = 0.01), suggesting good construct validity. Conclusion: Overall, the present study supports the continued use of the FDSS as a reliable and valid instrument to measure fatigue and daytime sleepiness in patients with DM1 for either clinical or research purposes. (C) 2017 Elsevier B.V. All rights reserved.