LAUSR

The study by Dubessy et al.1 is valuable for its instrumental analysis of sleep, despite the small and cross-sectional design, because it shows a large overlap between sleepiness and fatigue and discloses a subgroup with central-like hypersomnia. We studied 86 patients with MS by polysomnography (PSG) and the maintenance of a wakefulness test (MWT). Dubessy et al. did not identify a consistent group of patients with excessive daytime sleepiness (EDS) and without fatigue. Similarly, only 13% of our sample showed EDS without fatigue. In our sample, fatigue overlapped greater with depression than with EDS. Dubessy et al. excluded depressed patients, exposing their study to a selection bias.