Effects of left DLPFC versus right PPC tDCS on multiple sclerosis fatigue

Fatigue is a frequent and debilitating symptom in patients with multiple sclerosis (MS). Its classical treatments are still faced with limited benefits and numerous side effects. Hence, we aimed to evaluate the effects of transcranial direct current stimulation (tDCS), a noninvasive brain stimulation technique, on such a challenging symptom. Our secondary outcomes included the assessment of tDCS impact on mood and attentional performance.

Ten fatigued MS patients were enrolled in a double-blind, sham-controlled, and cross-over study. Each patient randomly received three anodal tDCS blocks: active stimulation over the left dorsolateral prefrontal cortex (DLPFC), active stimulation over the right posterior parietal cortex (PPC), and sham stimulation over either cortical site. Both cortical targets are key components in the MS fatigue networks. The blocks consisted of five consecutive daily sessions and were held apart by a washout interval of three weeks.

Only active left DLPFC stimulation significantly ameliorated fatigue. Mood improvement was exclusively obtained following active right PPC stimulation. Neither intervention had effects on attention.

Our study supports the role of anodal tDCS over the left prefrontal in treating MS fatigue. The lack of tDCS effects on attention might be related to the heterogeneity of the studied cohort, the relatively small sample size, the protocol design and duration. Modifying these variables and coupling tDCS with neuroimaging might improve the clinical outcomes and enhance our understanding of the tDCS mechanism of actions.