Fatigue is the most frequent complaint of MS patients, even those with low Expanded Disability Status Scale (EDSS) scores.  Fatigue affects quality of life for many individuals and is the main burden on the health and socioeconomic system.  Two studies with longitudinal evaluation over 2 years analyzed variables in regard to fatigue in MS.

In the study from the Karolinska Institutet in Stockholm, Sweden,219 outpatients were assessed every 6 months with the Fatigue Severity Scale (FSS). Personal and environmental factors (sex, age, sense of coherence, living with a partner, living with children, work status, and immunomodulatory treatment) were correlated.

The results showed that the FSS varied over the 2 years, with 54% changing FSS category 1 or several times.  Twenty-seven percent were persistently fatigued and 19% never fatigued.  In those patients who had increased or persistent fatigue, mood and disease-related factors were significantly different: depression (P = .001), weak sense of coherence (P = .02), living with a partner vs not living with a partner (P = .02), not working (P = .05), more than 10 years since the diagnosis of MS and with a moderate EDSS score compared with a mild EDSS (P = .001), more than 10 years since the diagnosis of MS and with a moderate EDSS compared with a severe EDSS score (P = .02), and a moderately progressive course compared with a mild course (P = .001).  

The conclusions of this study were that fatigue persistently affected at least 27% of the MS population and that those with a moderate course were at greatest risk, especially with an associated depression.

Another longitudinal study of fatigue showed that depression and physical impairment were significantly associated with persistent fatigue in a group of 267 MS patients followed over 2 years.  

Persistent and sporadic fatigue were not associated with disease duration, but they were significantly associated with physical impairment, primary progressive MS, insomnia, heat-sensitive fatigue, sudden-onset fatigue, and mood disturbance.