Fatigue, sleepiness, and physical activity in patients with multiple sclerosis

Fatigue is a frequent and disabling symptom in patients with multiple sclerosis (MS). The objective of the study was to compare fatigue and sleepiness in MS, and their relationship to physical activity. Eighty patients with MS rated the extent of experienced fatigue (Fatigue Severity Scale, FSS) and sleepiness (Epworth Sleepiness Scale, ESS). The relationship between the scales was analysed for the scales as a whole and for single items. The clinical status of the patients was measured with the Extended Disability Status Scale (EDSS). In addition, physical activity was recorded continuously for 1 week by wrist actigraphy. The mean scores of fatigue and sleepiness were significantly correlated (FSS vs. ESS r=0.42). Single item analysis suggests that fatigue and sleepiness converge for situations that demand self-paced activation, while they differ for situations in which external cues contribute to the level of activation. While fatigue correlated significantly with age (r=0.40), disease severity (EDSS, r=0.38), and disease duration (r=0.25), this was not the case for sleepiness. Single patient analysis showed a larger scatter of sleepiness scores in fatigued patients (FSS>4) than in non-fatigued patients. Probably, there is a subgroup of MS patients with sleep disturbances that rate high on ESS and FSS. The amount of physical activity, which was measured actigraphically, decreased with disease severity (EDSS) while it did not correlate with fatigue or sleepiness.