Modulation of alertness by sustained cognitive demand in MS as surrogate measure of fatigue and fatigability

Aim: Fatigue is a common, but vaguely defined symptom in MS. The aim of our study was to assess fatigue in the sense of performance at rest and fatigability after cognitive load objectively (Kluger, Krupp, & Enoka, 2013)(Kluger et al. 2013). Method: Alertness was measured in fifteen controls and thirty patients with Multiple Sclerosis and cognitive fatigue according to the Fatigue Scale for Motor and Cognition (FSMC) at rest (t1), after a 2.5 hours lasting test battery (t2) and one hour later (t3). The test battery was used as standardized cognitive load. Epworth Sleepiness Scale and Beck Depression Inventory were used for exclusion of common causes of secondary fatigue. Results: Reaction times at rest were 401 msec in patients, compared to 208 msec in controls. Reaction times increased in patients significantly and dramatically after the cognitive load (t2) and recovered slowly in most of the patients at t3. Normal volunteers did not show any increase in reaction times. Patients showed a significant correlation between self-estimation of fatigue (FSMC) and reaction times. Conclusion: Alertness at rest appears to be a surrogate marker for fatigue. Alertness after cognitive load represents change of performance or fatigability. Knowledge of recovery of alertness offers further opportunities for management of fatigue