Efectiveness of transcranial Direct Current Stimulation (tDCS) on Parkinson´s Disease (PD)-related pain: effects on pain processing features in PD patients

Abstract Background: PD-related pain is a prevalent and under-reported non-motor symptom that severely impacts patients' quality of life. Nevertheless, there is a lack of non-pharmacologic protocols to manage this symptom. Regarding their pain processing features, PD patients have reduced pain thresholds (PT), an augmented Temporal Summation (TS) after repetitive nociceptive stimulus, and the impairment of their Conditioned Pain Modulation (CPM) is correlated with greater severity and premature onset of the disease. Both pain and PD cause a reduction in corticomotor excitability, governed by the primary motor cortex (M1). TDCS applied to M1 increases corticospinal excitability, not only in the stimulated area but also in sensory and emotional pain processing structures. TDCS would be effective in treating central sensitivity-related pain, however, it has not been tested yet in PD-related pain. Objective: To estimate the effectiveness of tDCS on pain processing features in PD patients. Methods: This is a randomized, triple-blind, parallel design clinical trial with 18 subjects (61.3±11.52 years old). They were randomly assigned to one of two intervention groups: active-tDCS (9) vs. sham-tDCS (9). The active group received 10 consecutive sessions of 20 min of tDCS with active anode on M1 at 2 mA intensity. The sham group followed the same protocol, but the tDCS stimulator was turned off at 30 seconds. All subjects were evaluated pre, post, and 15 days post-intervention with the variables Pain Expansion (the sum of PTs), TS, and CPM. Results: There are statistically significant improvements between groups post-intervention for CPM (p=0.010), and 15 days post-intervention for CPM (p=0.032) and Pain Expansion (p=0.022) in favor of active-tDCS when compared with sham-tDCS. There are no statistically significant differences in the group-time interaction for the TS (p= 0.780). Research Category and Technology and Methods Clinical Research: 9. Transcranial Direct Current Stimulation (tDCS) Keywords: tDCS, Parkinson´s Disease, Pain Expansion, Conditioned Pain Modulation