Different cortical underpinnings for fatigue and depression in MS?

Fatigue is a common complaint in MS patients but its origins are still not fully understood. A major difficulty is that fatigue seems strongly correlated with depression.

95 MS patients and 15 healthy control subjects were included. The Fatigue Severity Scale and Beck's Depression Inventory were used to assess symptom-severity and to determine group membership for five groups: MS patients with and without fatigue, and with or without depressive mood, healthy controls. Participants were scanned using high-resolution structural 3D T1-weighted imaging. Cortical thickness for 84 areas was calculated using the NeuroQLab software in combination with the atlas for the Automated Anatomical Labeling software. A stepwise forward regression analysis was performed to predict group membership of the MS patients by thickness of cortical areas. We also performed a series of post-hoc ANOVAs to explore differences between the four patients groups and the healthy controls.

About 20% of the patients suffered only from fatigue or only from depressive mood. Regression analysis explained 17.3% of the variance and thickness of the right inferior parietal cortex, middle temporal pole and parahippocampus contributed significantly to the model. Patients with pure fatigue showed a specific decrease in cortical thickness in the inferior parietal lobe, patients with both depressive mood and fatigue in the right middle temporal pole. Additional ANOVAs revealed cortical thinning in the right middle cingulate cortex in the group with pure fatigue as well as the groups with depression.

Fatigue and depression can be dissociated in larger MS-patient groups using questionnaires and cortical thickness measures, but the cortical thickness measures only explain a small portion of variance of these neuropsychiatric symptoms.