New perspectives on pain management in rehabilitation

Introduction. Pain is a complex and debilitating experience. When pain lasts over three months it becomes chronic, outlasts normal tissue healing time and doesn’t serve to protective function. Patients with chronic pain no longer exhibit peripheral tissue damage but continue to feel pain, suggesting an abnormal functioning of the somatosensory system. This process may be due to central sensitization (CS), neuroplastic changes that occur in pain related central networks and boost pain perception independent of peripheral neural activation. Non-invasive brain stimulation (NIBS) seems to reduce chronic pain by directly altering brain activity. Trasncranial direct current stimulation (tDCS), one of the most used NIBS techniques, seems to be efficacy in reducing chronic pain, when used alone or in combination with other treatments. Aim of this PhD project is to investigate efficacy of brain stimulation techniques on chronic pain, specifically due to temporomandibular disorders (TMDs) and low back pain (LBP). Furthermore, we would identify biomarkers related to chronic pain, using electroencephalography and pain threshold assessment in people with chronic orofacial pain. Methods. In the first research project we proposed tDCS treatment in people with chronic pain due to TMDs. Stimulation was delivered for five consecutive days over primary motor cortex for 20 minutes a day with the intensity of 2mA. Subjects were evaluated before and after treatment and at one-month follow-up for pain perception and psychological symptoms. In the second research project tDCS was combined with group exercise treatment and proposed to people with chronic LBP. Stimulation parameters and assessment points were the same. In the third research project we evaluated people with orofacial pain due to TMDs using EEG recording and pain threshold assessment looking for CS signs. Results. Our findings support the use of tDCS on patients with chronic pain due to TMDs. The majority of the sample had good results for pain intensity and depressive symptoms. One case, who had severe degenerative disease, did not report any beneficial effects after tDCS. Also in subjects with chronic LBP tDCS seems to be effective in ameliorating pain and psychological wellbeing, but the effects were evident only at one-month follow-up when combined with behavioural intervention. Reduced pain threshold and increased gamma activity in frontal and central brain areas were recorded in people with TMDs as chronic pain’s biomarkers. Discussion and Conclusion. NIBS can be used to reverse maladaptive changes that occur in chronic pain. In people with chronic pain due to TMDs or LBP, tDCS seems to be efficacy on symptoms intensity and pain- related quality of life. tDCS efficacy may be improved combining its top-down effects with a bottom-up approach. Brain modifications due to chronic pain and presence of CS mechanisms can be assessed using EEG. Abnormal EEG activity in central and frontal areas during pain threshold assessment may be recorded as CS signs in people with chronic pain. Interpretation of our findings needs to be confirmed by further studies on people with chronic pain.