The present study aims to investigate the effect of a Unihemispheric Concurrent Dual-Site anodal Transcranial Direct Current Stimulation combined with therapeutic exercise on pain in subjects with FM.

Fibromyalgia (FM) syndrome is characterized as a cardinal symptom of chronic pain. It is one of the rheumatic diseases with the greatest impact on quality of life.

Although the etiology and pathophysiology are not yet completely clear, FM is related to specific changes in brain activity, such as a decrease in blood flow in the thalamus, caudate nucleus and pons tegmentum. This could be related to the appearance of a disorder in pain regulation, characterized by an alteration of the sensory and pain process in the central nervous system, due to neuroplastic changes in the neural circuits related to pain. Imaging studies have shown that FM could be associated with functional changes in the brain, such as a reduction in connectivity in efferent pain inhibitory pathways and central sensitization in afferent pain pathways, resulting in an increase in pain perception.

The most common FM treatment guidelines recommend aerobic exercise as the only non-pharmacological therapy with level A recommendation in the treatment of FM. In the same way, it concludes that it is more than recommended to combine therapies assuming synergistic effects between them.

Neuromodulation treatments with transcranial direct current stimulation (tDCS) have been shown to induce significant analgesia in FM through the modification of sensory processing of pain by thalamic inhibitory circuits. To date, the few studies that have combined tDCS and therapeutic exercise in FM have applied tDCS to the primary motor cortex (M1) in isolation. Currently, several studies conclude that Unihemispheric Concurrent Dual-Site anodal Transcranial Direct Current Stimulation (UHCDS a-tDCS) on the dorsolateral prefrontal cortex (DLPFC) and M1 produces a 50% greater modulation of corticospinal excitability in healthy subjects. To date, there is no study that has evaluated the effectiveness of this novel application of tDCS in subjects with FM on pain.

Inclusion Criteria:

• Age between 18 and 65 years.
• Fulfilled the 2010 American Colleague of Rheumatology criteria for fibromyalgia.
• Usual pain intensity of 4 or more points on a visual analogue scale.
• Able to participated in a therapeutic exercise program.
• Understanding of spoken and written Spanish.

Exclusion Criteria:

• Pregnancy or breastfeeding.
• Metallic implants in the head.
• Tumor, trauma or surgery in the brain.
• Epilepsy or stroke.
• History of substance abuse in the last 6 months.
• Use of carbamazepine in the last 6 months.
• Diagnosed psychiatric pathology.
• Rheumatic pathology not medically controlled.
• Coexisting autoimmune pathology.
• Chronic inflammatory disease (rheumatoid arthritis, erythematosus systemic lupus, inflammatory bowel disease).