Anodal transcranial direct current stimulation of the motor cortex ameliorates chronic pain and reduces short intracortical inhibition.
BACKGROUND
Consecutive sessions of transcranial direct current stimulation (tDCS) over the primary motor cortex (M1) may be a suitable therapy to treat chronic pain, as it can modulate neural activities in the stimulated and interconnected regions.


OBJECTIVE
The present study investigated the analgesic effect of five consecutive days of anodal/sham tDCS using subjective (visual analog scale [VAS]) and objective (cortical excitability measured by transcranial magnetic stimulation [TMS]) measurements.


METHODS
Patients with therapy-resistant chronic pain syndromes (trigeminal neuralgia, poststroke pain syndrome, back pain, fibromyalgia) participated. As this clinical trial was an exploratory study, statistical analyses implemented exploratory methods. Twelve patients, who underwent both anodal and sham tDCS, were analyzed using a crossover design. An additional nine patients had only anodal or sham stimulation. tDCS was applied over the hand area of the M1 for 20 minutes, at 1mA for five consecutive days, using a randomized, double-blind design. Pain was assessed daily using a VAS rating for one month before, during, and one month post-stimulation. M1 excitability was determined using paired-pulse TMS.


RESULTS
Anodal tDCS led to a greater improvement in VAS ratings than sham tDCS, evident even three to four weeks post-treatment. Decreased intracortical inhibition was demonstrated after anodal stimulation, indicating changes in cortico-cortical excitability. No patient experienced severe adverse effects; seven patients suffered from light headache after anodal and six after sham stimulation.


CONCLUSIONS
Results confirm that five daily sessions of tDCS over the hand area of the M1 can produce long-lasting pain relief in patients with chronic pain.
Antal
Andrea
A
Department of Clinical Neurophysiology, Georg-August University, 37075 Göttingen, Germany. Aantal@gwdg.de
Terney
Daniella
D
Kühnl
Stefanie
S
Paulus
Walter
W
D000328:Adult; D000368:Aged; D000698:Analgesia / Q000379:methods*; D000704:Analysis of Variance; D002908:Chronic Disease / Q000628:therapy; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004599:Electric Stimulation Therapy; D004566:Electrodes; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000503:physiopathology*; D009433:Neural Inhibition; D059408:Pain Management; D010147:Pain Measurement; D017288:Pain Threshold; D050781:Transcranial Magnetic Stimulation; D016896:Treatment Outcome