Effects of Transcranial Direct Current Stimulation (tDCS) on Patients With Chronic Orofacial Pain

Effects of Transcranial Direct Current Stimulation (tDCS) in Patients With Chronic Orofacial Pain Unresponsive to Conventional Treatment. A Randomized Controlled Trial.

Patients affected by chronic orofacial pain represent an emergent medical problem due to the lack of knowledge on the cause, pathophysiology and psychology of many of these conditions, that belongs to a multifactorial origin. Particularly, temporomandibular joint disorders involve a series of symptoms that refers both to intrinsic and extrinsic joint conditions where pain can be associated to a reduction of the joint movement, click or to other sounds of the joint. The lack of a recognized causal therapy led to the suggestion of many treatment modalities with a multidisciplinary approach for the management of symptoms that include the use of occlusal splints, physiotherapy-speech therapy, behavioral and physical therapy, drugs, chirurgical approaches. In most cases these strategies together allow the control of the symptoms, even though they aren't completely resolutive. In these patients is frequent chronic pain and ineffectiveness of common drugs used. It has been demonstrated how transcranial electrical brain stimulation with direct current (tDCS) is able to reduce the intensity and the duration of chronic pain. Stimulating the motor cortex can reduce pain by modulating brain activities in the areas involved in cerebral circuits controlling pain, such as thalamus, facilitating the descendant inhibitory mechanisms and enhancing the number of opiates receptors. This clinical trial is based on the evaluation of the effects of tDCS on pain and on activities daily living (ADL) participation patients with chronic orofacial pain that don't respond to other treatments.

Inclusion criteria: Male and female between 18 and 75 years old Clinic history of previous orofacial and/or dental surgery Chronic orofacial pain for more than a year measurable by the VAS more than 3 . Pain not responsive to pharmacological treatment (analgesic, anti inflammatory, opiaces, antidepressant drugs and physiotherapy modalities) Outcome measures: Subjects will be assessed before the beginning of the treatment (T0), after tDCS (T1) and after one month of stimulation(T2) . In the two weeks prior to T0 the patient will be asked in a questionnaire to report daily the level of pain, anxiety and state of mind using the VAS. This period of observation is necessary for the patient to get used to these measures and to underline possible intra-subject changing. • Clinic scales -Visual Analogue Scale (VAS): it is one of the most used between scales for pain evaluation [18] RDC/TMD AXIS I: diagnostic classification for temporomandibolar disfunction. RDC/TMD AXIS II: behavioral questionnaire (7 questions about chronic pain severity) which evaluates chronic pain following the graded scale for chronic pain. Symptoms Checklist-90-R scales (SCL 90-R): Depression and anxiety assessment for non-specific physical symptoms electrical pain threshold: The Digitimer High Voltage Stimulator model DS74 provides high voltage pulses of constant current up to 100mA, pulses are of short duration and the output current is variable ranging between 0 and 100mA. The Digitimer is used to evaluate the pain perception threshold by applying electrical stimulation to the index finger to a pulse duration of 200 ls. The initial current applied is 0mA and increases of 0.1 mA until the subject feels pain. Oral Health Impact Profile 49 (OHIP 49): provides a measure of social impact of oral disorders by providing a comprehensive measure of dysfunction, discomfort and disability resulting from the oral cavity conditions. The OHIP-49 is based on the adaptation of the World Health Organization classification. Pain detect Questionnaire Pressor pain threshold

This group will receive sham-tDCS for 5 days. The anode will be placed on the primary motor cortex (M1) of the dominant hemisphere and the cathode on the contralateral supraorbital area. The direct current is transmitted through a pair of sponge electrodes, with a surface of 35 cm2 (7x5), soaked in saline solution and, it is generated by a constant current stimulator, with rechargeable batteries. This continuous stimulation lasted 30 seconds, with an intensity of 1 milliampere.

This group will receive continuous stimulation lasting 20 minutes daily, for 5 days. Transcranial direct current stimulation (tDCS) will be administered as follows. The anode will be placed on the primary motor cortex (M1) of the dominant hemisphere and the cathode on the contralateral supraorbital area. The direct current is transmitted through a pair of sponge electrodes, with a surface of 35 cm2 (7x5), soaked in saline solution and, it is generated by a constant current stimulator, with rechargeable batteries. This continuous stimulation lasted 20 minutes, with an intensity of 1 milliampere.

Visual analogue scale measure for pain. Score range from 0-10. For rating overall pain: mild = 1-3, moderate = 4-7, severe = 8-10 For rating Chronic Pain, excellent internal consistency for a single pair of rating between Numeric Pain Rating Scale and Visual Analogue Scale (r = 0.86)

1) one day pre-tDCS 5 days treatment. 2) Every day, for 5 days pre and post tDCS stimulation. 3) one day post tDCS 5 days treatment. 4)Follow up at one month.

Behavioral questionnaire (7 questions about chronic pain severity) which evaluates chronic pain following the graded scale for chronic pain.

The device for assessing pain is a high voltage stimulator provides high voltage pulses of constant current up to 100 milliampere, pulses are of short duration and the output current is variable ranging between 0 and 100 milliampere. This device is used to evaluate the pain perception threshold by applying electrical stimulation to the index finger to a pulse duration of 200 ls. The initial current applied is 0 milliampere and increases of 0.1 milliampere until the subject feels pain.

Provides a measure of social impact of oral disorders by providing a comprehensive measure of dysfunction, discomfort and disability resulting from the oral cavity conditions. The OHIP-49 is based on the adaptation of the World Health Organization classification.

The PD-Q is a reliable screening tool with high sensitivity, specificity and positive predictive accuracy. Simple, patient-based, easy-to-use screening questionnaires can determine the prevalence of neuropathic pain components both in individual low back pain patients and in heterogeneous cohorts of such patients. Since NeP correlates with more intense pain, more severe co-morbidity and poorer quality of life, accurate diagnosis is a milestone in choosing appropriate therapy.

Inclusion Criteria: Male and female between 18 and 75 years old Clinic history of previous orofacial and/or dental surgery Chronic orofacial pain for more than a year measurable by the VAS more than 3 . Pain not responsive to pharmacological treatment (analgesic, anti inflammatory, opiates, antidepressant drugs and physiotherapy modalities) Exclusion Criteria: Contraindication to tDCS: presence of metallic implants that can be stimulated, moved or overheated by electric current, positive anamnesis for epilepsy, implantable systems ( ventriculoperitoneal shunt, pacemaker, intracranial pumps, intracranial metallic systems) Major neurological or psychiatric pathologies Pregnancy Severe hepatorenal and cardiopulmonary diseases