A case of refractory orofacial pain treated by transcranial direct current stimulation applied over hand motor area in combination with NMDA agonist drug intake.

BACKGROUND: A female patient presented with persistent orofacial pain on the right side for 3 years, attributed to a viral infection. The pain had remained largely pharmacoresistant, reaching a value of 8/10 on the visual analogue scale.
METHODS: The patient underwent varying three different conditions of trancranial direct current stimulation (tDCS). First, the contralateral representational field of the face area of the primary motor cortex (M1) was anodally stimulated for 5 consecutive days for 20 minutes at 1 mA. During the second stimulation condition, 20 minutes cathodal stimulation was applied for 5 consecutive days at 2 mA intensity over the contralateral representational field the face area of primary somatosensory cortex (SI). In the third condition, the hand area of the left M1 was anodally stimulated for 20 minutes at 1 mA intensity for 8 days combined with the oral administration of D-cycloserine.
RESULTS: With regard the third stimulation condition, a 60% reduction in pain perception was observed toward the end of the stimulation. The patient reported a significant pain relief sensation for up to 6 weeks poststimulation.
CONCLUSIONS: Although this is a pilot exploratory trial in a single patient, our study is a further step toward clinical application of tDCS over the M1 using pharmacologic intervention, to prolong the induced after effect. Furthermore, it demonstrates the potential for repetitive daily stimulation therapy for chronic pain patients.