Analgesic effect of cathodal transcranial current stimulation over right dorsolateral prefrontal cortex in subjects with muscular temporomandibular disorders: study protocol for a randomized controlled trial

BACKGROUND: Temporomandibular disorders are a group of orofacial pain conditions that are commonly identified in the general population. Like many other chronic pain conditions, they can be associated with anxiety/depression, which can be related to changes in the activity of the dorsolateral prefrontal cortex. Some studies have demonstrated clinical improvement in subjects with chronic pain who are given therapeutic neuromodulation. Transcranial direct current stimulation is a noninvasive brain stimulation technique that allows the modulation of neuronal membranes. This therapy can enhance or inhibit action potential generation in cortical neurons. In some instances, medications acting in the central nervous system may be helpful despite their adverse side effects. It is important to determine if cathodal transcranial direct current stimulation over the dorsolateral prefrontal cortex, an area that modulates emotion and motor cortex excitability, has an analgesic effect on chronic temporomandibular disorders pain. METHOD/DESIGN: The investigators will run a randomized, controlled crossover double blind study with 15 chronic muscular temporomandibular disorder subjects. Each subject will undergo active (1 mA and 2 mA) and sham transcranial direct current stimulation. Inclusion criteria will be determined by the Research Diagnostic Criteria for Temporomandibular Disorders questionnaire, with subjects who have a pain visual analogic scale score of greater than 4/10 and whose pain has been present for the previous 6 months, and with a State-Trait Anxiety Inventory score of more than 42. The influence of transcranial direct current stimulation will be assessed through a visual analogic scale, quantitative sensory testing, quantitative electroencephalogram, and the State-Trait Anxiety Inventory score. DISCUSSION: Some studies have demonstrated a strong association between anxiety/depression and chronic pain, where one may be the cause of the other. This is especially true in chronic temporomandibular disorders, and breaking this cycle may have an effect over the symptoms and associated dysfunction. We believe that by inhibiting activity of the dorsolateral prefrontal cortex though cathodal transcranial direct current stimulation, there may be a change in both anxiety/depression and pain level. Transcranial direct current stimulation may emerge as a new tool to be considered for managing these patients. We envision that the information obtained from this study will provide a better understanding of the management of chronic temporomandibular disorders. TRIAL REGISTRATION: This trial was registered at clinicaltrials.gov on 24 May 2014 (Identifier: NCT02152267).