Transcranial direct current stimulation: A glimmer of hope for multiple sclerosis fatigue?

Multiple sclerosis (MS) is a neurological disease of the central nervous system characterized by inflammation, demyelination and neurodegeneration. Throughout the disease process, patients may complain of a panel of sensory, motor, cognitive and behavioral symptoms. Fatigue is a debilitating manifestation of central nervous system diseases with physical, cognitive and psychosocial dimensions. In MS, fatigue could be very frequent concerning up to 90% of patients and may have a drastic impact on their quality of life. Based on neuroimaging studies, a 'cortico-striato-thalamo-cortical' loop seems to underlie this symptom. Despite the availability of pharmacological molecules, the majority of them fail to bring satisfactory outcomes mainly because of the numerous related side-effects. Therefore, finding a safe, easy to implement, and effective alternative therapy is highly needed. These properties appear to match those of noninvasive brain stimulation techniques such as transcranial direct current stimulation (tDCS). tDCS consists of placing two electrodes over cortical sites, such as those that take part in MS fatigue loop. Here, tDCS protocols targeting MS fatigue are revisited. Their short and long-term effects are discussed. The majority of the available protocols have applied 5 consecutive daily 20-min sessions of anodal tDCS over specific cortical sites and yielded beneficial effects on MS fatigue. Finally, the recent emergence of remotely supervised tDCS protocols are also tackled in this work aiming to address the future possibility of translating the current research data into routine clinical practice. This may lead to optimize patients' care and improve their quality of life.