The Role of Central Sensitization in Responsiveness to Brain Stimulation for Patients with Nonspecific Chronic Low Back Pain – An Exploratory Study

Sharon Wang-Price,1 Jason Zafereo,2 Khalid Alkhathami,3,* Yousef Alshehre,4,* Hui-Ting Goh1 1School of Physical Therapy, College of Health Sciences, Texas Woman’s University, Dallas, TX, USA; 2Department of Physical Therapy, University of Texas Southwestern Medical Center, Dallas, TX, USA; 3Department of Health Rehabilitation, College of Applied Medical Sciences, Shaqra University, Shaqra, Saudi Arabia; 4Department of Health Rehabilitation Sciences, Faculty of Applied Medical Sciences, University of Tabuk, Tabuk, Saudi Arabia*These authors contributed equally to this workCorrespondence: Sharon Wang-Price, School of Physical Therapy, College of Health Sciences, Texas Woman’s University, Texas Woman’s University, 5500 Southwestern Medical Ave., Dallas, TX, 75235-7299, USA, Email swang@twu.eduPurpose: This exploratory study aimed to examine (1) the effects of a single session of repetitive transcranial magnetic stimulation (rTMS) on pain thresholds in patients with high vs. low central sensitization (CS) levels, and (2) whether individuals with high vs. low CS levels exhibit different cortical excitability responses to rTMS compared with age- and sex-matched asymptomatic controls.Patients and Methods: Twenty participants who had low back pain (LBP) for longer than 6 months were dichotomized into the high CS group (n = 10) and the low CS group (n = 10) using a Central Sensitization Inventory cutoff score of 33.5. In addition, 16 age- and sex-matched asymptomatic controls (8 for each CS group) were enrolled. Outcome measures, including pressure pain threshold (PPT), thermal pain threshold, and motor evoked potential (MEP) were collected before and after a single session of rTMS (10 Hz, 10-second pulse trains with a 50-second inter-train interval for 20 minutes). Non-parametric statistics were performed for within-group and between-group comparisons with p < 0.05 for significance.Results: Only the high CS group had significantly improved PPTs after rTMS (p = 0.037), with a moderate effect size. The low CS group and both matched asymptomatic control groups had an increase of MEPs after rTMS, whereas the high CS group had a decrease of MEPs after rTMS, although none of these MEP changes were statistically significant.Conclusion: This study identifies a patient population that may benefit from rTMS for reduction of pressure sensitivity. The decreased sensitivity to pressure in participants with high levels of CS corresponded to a decrease of cortical excitability after rTMS, which was in contrast with the rTMS effects observed in participants with low levels of CS and asymptomatic controls.Plain Language Summary: Central sensitization is a phenomenon that may be an underlying mechanism contributing to chronic pain in some patients. This article explores whether a single session of non-invasive brain stimulation would affect pain sensitivity and brain activity in patients who have different levels of central sensitization. We examined 20 participants who had LBP for longer than 6 months and divided them into two groups, a high CS group and a low CS group, based on their scores on the Central Sensitization Inventory questionnaire. In addition, we enrolled 16 age- and sex-matched asymptomatic controls (8 for each CS group) for the study. We collected pressure pain threshold (PPT), thermal pain threshold and motor evoked potential (MEP) from each participant before and after a single session of non-invasive brain stimulation. The results indicate that non-invasive brain stimulation may reduce sensitivity to pressure in patients with high levels of central sensitization. In addition, patients with high and low levels of central sensitization appeared to respond differently to non-invasive brain stimulation.Keywords: transcranial magnetic stimulation, pressure pain threshold, thermal pain threshold, hypersensitivity, lumbar spine