Objective: To investigate whether active anodal transcranial direct current stimulation (tDCS) (of dorsolateral prefrontal cortex [DLPFC] and primary motor cortex [M1]) as compared to sham treatment is associated with changes in sleep structure in fibromyalgia.
Methods: Thirty-two patients were randomized to receive sham stimulation or active tDCS with the anode centered over M1 or DLPFC (2 mA, 20 minutes for five consecutive days). A blinded evaluator rated the clinical symptoms of fibromyalgia. All-night polysomnography was performed before and after five consecutive sessions of tDCS.
Results: Anodal tDCS had an effect on sleep and pain that was specific to the site of stimulation: such as that M1 and DLPFC treatments induced opposite effects on sleep and pain, whereas sham stimulation induced no significant sleep or pain changes. Specifically, whereas M1 treatment increased sleep efficiency (by 11.8%, P = 0.004) and decreased arousals (by 35.0%, P = 0.001), DLPFC stimulation was associated with a decrease in sleep efficiency (by 7.5%, P = 0.02), an increase in rapid eye movement (REM) and sleep latency (by 47.7%, P = 0.0002, and 133.4%, P = 0.02, respectively). In addition, a decrease in REM latency and increase in sleep efficiency were associated with an improvement in fibromyalgia symptoms (as indexed by the Fibromyalgia Impact Questionnaire). Finally, patients with higher body mass index had the worse sleep outcome as indexed by sleep efficiency changes after M1 stimulation.
Interpretation: Our findings suggest that one possible mechanism to explain the therapeutic effects of tDCS in fibromyalgia is via sleep modulation that is specific to modulation of primary M1 activity.