In multiple sclerosis (MS), fatigue is the most prevalent cause of impaired ability to work. In narcolepsy, daytime sleepiness is the main symptom but some studies indicate fatigue being present. We aimed to assess fatigue and associated features in patients with MS or narcolepsy and healthy controls and to assess whether clinical parameters separate fatigued (MS-F) and non-fatigued MS patients (MS-NoF).
Materials & Methods
In this non-interventional cross-sectional study, we recruited 34 MS patients, 15 narcolepsy type 1 patients and 17 healthy controls. An interviewer administered the Fatigue Severity Scale (FSS), the Insomnia Severity Index (ISI), the Epworth Sleepiness Scale, the Patient Health Questionnaire-9 and the Saltin-Grimby Physical Activity Level Scale. Information about clinical parameters and current treatments was collected.
In its fatigue profile, MS-F resembled the narcolepsy group rather than MS-NoF, which resembled the healthy control group. ISI alone was significantly associated with FSS, and only in MS-NoF and healthy controls; in MS-F and the narcolepsy group, no variable was associated with FSS. Months since diagnosis was the only clinical variable significantly separating MS-F from MS-NoF. In MS, disease duration correlated with fatigue. No clinical variables correlated with fatigue in the narcolepsy group.
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.