Sleep disorders in multiple sclerosis and their relationship to fatigue.

Treatment of multiple sclerosis (MS)-related fatigue is still a challenging task, given that no proven therapies exist and its mechanisms are not known. Our review highlights the relationship between MS-related fatigue and sleep disorders (SD). Although many studies suggest a higher overall prevalence of SD in MS, there are no valid and robust data to confirm this hypothesis until now except for restless legs syndrome (RLS): the prevalence of RLS in MS patients-especially in those with severe pyramidal and sensory disability-seems to be four times higher than in controls subjects. RLS is sometimes difficult to distinguish from spasticity and in case of doubt, probatory dopaminergic therapy or polysomnographic (PSG) investigations may be helpful. Nocturia may impact MS-related fatigue and should be considered. The treatment of underlying SD led to an improvement of MS-related fatigue. From a scientific point of view, SD should be examined in all studies investigating MS-related fatigue and be considered as a relevant confounder.