MRI Multiparameter measures as relevant explanatory variables of cognitive but not physical fatigue in Multiple Sclerosis

Introduction: Fatigue symptoms are highly frequent in patients with multiple sclerosis (MS). However, the underlying brain and clinical mechanisms associated specifically to feeling of cognitive and physical fatigue remain largely misunderstood.
Aim of study: To investigate whether subjective cognitive and physical fatigue depend on different sets of brain and clinical variables in MS.
Methods: Multiparameter mapping (MPM) MRI data (R1 parameter in central grey matter (GM), R2 in cortical and central GM, R2 in cortical white matter (WM), PD in central GM and in cortical WM), and clinical data (age, depression, anxiety, cognitive and physical fatigue scores at the M-FIS; disease duration and EDSS score for patients) were collected among MS patients (n=35) and healthy controls (n=28). Stepwise regression analysis for the cognitive and physical sub-scores of the M-FIS were performed in each group, using clinical and MRI variables.
Results: Variance of cognitive M-FIS score for patients was explained with a model taking into account anxiety, depression and measures of cortical and central grey matter (R² = 0.5397, p < .0001). For controls, the model included age, depression and R2 parameter in cortical white matter (R²=0.4137, p = 0.0045). The model with physical M-FIS score included EDSS and anxiety for patients (R² = 0.3834, p = 0.0004), but age and depression for controls (R²= 0.4908, p = 0.0002).
Conclusions: These results suggest (1) that the determinants of subjective fatigue vary between MS and control participants; (2) that only cognitive fatigue is linked to brain characteristics. These results stress the need to study cognitive and physical fatigue as two separate entities in MS.