High-Definition and Non-invasive Brain Modulation of Pain and Motor Dysfunction in Chronic TMD

Abstract

Background: Temporomandibular disorders (TMD) have a high prevalence and in many patients pain and masticatory dysfunction persist despite a range of treatments. Non-invasive brain neuromodulatory methods, namely transcranial direct current stimulation (tDCS), can provide relatively long-lasting pain relief in chronic pain patients.

Objective: To define the neuromodulatory effect of five daily 2x2 motor cortex high-definition tDCS (HD-tDCS) sessions on clinical pain and motor measures in chronic TMD patients. It is predicted that M1 HD-tDCS will selectively modulate clinical measures, by showing greater analgesic after-effects compared to placebo, and active treatment will increase pain free jaw movement more than placebo.

Methods: Twenty-four females with chronic myofascial TMD pain underwent five daily, 20-min sessions of active or sham 2 milliamps (mA) HD-tDCS. Measurable outcomes included pain-free mouth opening, visual analog scale (VAS), sectional sensory-discriminative pain measures tracked by a mobile application, short form of the McGill Pain Questionnaire, and the Positive and Negative Affect Schedule. Follow-up occurred at one-week and four-weeks post-treatment.

Results: There were significant improvements for clinical pain and motor measurements in the active HD-tDCS group compared to the placebo group for: responders with pain relief above 50% in the VAS at four-week follow-up (P = 0.04); pain-free mouth opening at one-week follow-up (P < 0.01); and sectional pain area, intensity and their sum measures contralateral to putative M1 stimulation during the treatment week (P < 0.01). No changes in emotional values were shown between groups.

Conclusion: Putative M1 stimulation by HD-tDCS selectively improved meaningful clinical sensory-discriminative pain and motor measures during stimulation, and up to four-weeks post-treatment in chronic myofascial TMD pain patients.

Keywords: Clinical trial; Pain; PainTrek; Temporomandibular disorder; Transcranial direct current stimulation.

Figure 1

Example of a pain drawing in PainTrek. In this example, the pain is depicted as severe immediately anterior to the patient's right ear, moderate along the right zygoma and ramus of the mandible, and mild in the area of mandibular angle. All grey areas have no pain.

Figure 2

Figure caption: Brain modulation using 2×2 HD-tDCS Montage. A. 3D rendered head built from the MRI derived segmentation masks used in the study. Anode electrodes (red) were placed over C3 and C5 and Cathode electrodes were placed over FC3 and FC5. B. Skin,skull, and CSF masks are suppressed to reveal the underlying gray matter mask. C. Induced cortical surface electric-field directional plot for 2 mA stimulation. Red denotes inward (anodal) stimulation while blue denotes outward (cathodal) stimulation. D. Induced cortical surface electric-field magnitude plot for 2 mA stimulation.

Figure 3

PainTrek summary. Colors represent change in pain from baseline to one-month follow-up on the side of head contralateral to stimulation for each patient.