Fatigue, insomnia and daytime sleepiness in multiple sclerosis versus narcolepsy.

Fatigued MS patients resemble narcolepsy patients more than they resemble non-fatigued MS patients, who resemble healthy controls. Insomnia is the main factor associated with fatigue in MS, while disease duration is the only clinical variable separating fatigued and non-fatigued MS patients. In fatigued patients, variance in fatigue cannot be explained by insomnia, daytime sleepiness, depression or level of exercise.