Neurophysiologic Signatures of Trigeminal Neuralgia Pain

Trigeminal neuralgia (TN) is an extremely painful and highly disabling orofacial pain disorder, often referred to as the "suicide disease," for which presently available therapies are largely ineffective or inadequate. Both the unpredictable response to treatment and variability in long-term clinical outcomes in TN strongly suggest that a range of peripheral and central mechanisms remain to be understood. The long-term goal is to identify the mechanisms involved in the initiation and progression of TN, and uncover rational targets for the safe and effective treatment of TN. The objective of this application is to explore the use of multimodal neuroimaging and neurophysiologic techniques in defining neural signatures of the disease. Additionally, the study team wants to evaluate the efficacy of transcranial electrical stimulation on relieving pain. The rationale for the proposed research is that identification of signature peripheral and central activation sites will allow for individualized treatment strategies for TN patients.

To modulate brain activities the investigators will use transcranial electrical stimulation (tES). tES is an emerging neuromodulation technique that can be noninvasively and safely applied in humans. tES can help better understand the causal roles of brain networks and brain activities and has shown efficacy in improving pain. tES has two main variations: transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS). The former applies a weak direct current to the scalp whereas the latter applies a weak sinusoidal current to the scalp. tDCS can modulate the excitability of tissues under the stimulating electrodes. tACS is particularly suited for interacting with various oscillatory activities in the brain. tES has been used to study normal brain function and treat neurological and pain disorders as well. There is demonstrated efficacy in improvement of pain in subjects suffering from fibromyalgia and neuropathic pain. The study team will use different tDCS/tACS montages targeting different brain regions and observe behavior and neuronal activities. The current strength will be within 1mA or 2mA which has been shown to be safe and effective.

Inclusion criteria

• Healthy subjects who have been diagnosed with trigeminal neuralgia (TN) pain (ASA status 1, 2, or 3).
• Subjects diagnosed with TN pain must have average pain in the moderate to severe (Visual Analog Scale (VAS) of 30-100 mm) range. These subjects will be asked to stop their current medications for 24 hours prior to their scan.
• Patients diagnosed with classical trigeminal neuralgia, type 1 [TN1, G50.00], or symptomatic trigeminal neuralgia [TN2, G53.80] according to the International Classification of Headache (IHS) Disorders criteria (7).

Exclusion criteria

• Patients diagnosed with post-herpetic neuralgia, trigeminal neuropathic pain, and trigeminal deafferentation pain.
• TN subjects with ASA status 4-5 and Emergency operation.
• Presence of chronic disease (e.g. cardiovascular disease, liver disease, kidney disease, diabetes, etc.), other than trigeminal neuralgia.
• Pregnant females