Relation between cognitive fatigue and circadian or stress related cortisol levels in MS patients

Background Cortisol levels are increased in MS patients. However, the relation between cortisol, cognitive fatigue and load is still unknown and is investigated in this study. Method: In 40 MS patients and 20 healthy controls, cortisol levels were assessed (in saliva) in the morning and afternoon, before and after 5 runs of a cognitively demanding divided attention task (lasting in total 25-minutes). MS patients were divided in those suffering from cognitive fatigue (MS-F) or not (MS-NF). Results: MS-NF patients showed elevated cortisol levels in the morning and in the afternoon before the reaction time task compared to healthy controls. Differences in cortisol levels among the four measurements were also larger compared to healthy controls and MS-F patients. These differences could not be explained by medication, EDSS score, MS course, age or gender. MS-NF patients also produced more omissions on the attention task compared to healthy controls and MS-F patients. MS-F patients experienced more fatigue after the attention task, but they did not show a task related performance decline. Conclusion: MS-NF patients, and not MS-F patients, deviate in cortisol release and task performance from healthy controls and from MS-F patients. We suggest that MS-NF patients suffer from a dysregulation of their circadian cortisol level.