Evidence for Central Sensitization in Patients with Temporomandibular Disorders: A Systematic Review and Meta-analysis of Observational Studies

ObjectivesSeveral authors have evaluated different pain measurements, including quantitative sensory testing (QST), temporal summation (TS), and conditioned pain modulation (CPM) in order to determine the presence of central sensitization (CS) and its influence on patients with temporomandibular disorders (TMD). Since there are no convincing studies about this topic, the purpose of this study was to conduct a review of the studies involving CS-related measures in TMD patients. MethodsA meta-analysis of case-control and cohort/cross sectional studies was conducted. Standardized mean differences (SMD) and 95% confidence intervals (CIs) were calculated for relevant QST outcomes and pooled in a meta-analysis using the random effects model. Twenty-two studies (eleven case-control and eleven cross sectional studies) met the inclusion criteria; eight were included in the meta-analysis (five cross-sectional and three case-control). Patients with TMD had decreased pressure pain thresholds in both trigeminal (five studies; n = 1,985; SMD = -1.55, 95% CI -2.23 to -0.77; P < 0.01) and remote areas (five studies; n = 1,985; SMD = -1.92, 95% CI -2.95 to -0.89; P < 0.01). When analyzing for thermal hyperalgesia (hot and cold pain thresholds), differences were not found in trigeminal areas or remote areas in patients with TMD. The TS qualitative analysis showed strong evidence of spinal hyperexcitability for mechanically evoked pain. ConclusionThese meta-analyses support the existence of differences in widespread pressure pain sensitivity in patients with TMD when compared with asymptomatic subjects. Spinal and central hyperexcitability can be found in TMD patients as shown by an increase in mechanical TS.