Alterations in Surface Electromyography Are Associated with Subjective Masticatory Muscle Pain

Abstract

Background: Tenderness of masseters and temporalis can be considered a relevant tool for diagnosis of myo-type craniofacial pain disorders, but a limit of pain score systems is that they are based on subjective pain perception. Surface electromyography (sEMG) is a noninvasive and reliable tool for recording muscle activity. Therefore, we investigated whether a correlation exists between tenderness on masseters and temporalis, assessed by subjective pain scale, and muscles activity, evaluated by sEMG, in patients with painful temporomandibular disorder (TMD) and concurrent tension-type headache (TTH).

Methods: A cross-sectional study on fifty adult volunteer patients with TMD and TTH, who underwent tenderness protocol according to Diagnostic Criteria for TMD (DC/TMD) guidelines, was conducted followed by sEMG recording of temporalis and masseters. Pearson's correlation was performed to investigate the correlation between muscular activity and subjective pain scores.

Results: An overall moderate correlation between muscle tenderness and sEMG values (y = 1 + 1.2 · x; r 2 = 0.62; p < 0.0001), particularly in the temporalis, was observed. Segregation of data occurred according to tenderness and sEMG values. At the highest pain score, the mean sEMG absolute value was higher at the temporalis than the masseters.

Conclusions: Our study provides evidence that subjective pain perception can be objectively quantified at a magnitude proportional to pain severity. At greater tenderness scores, higher sEMG activity at the level of temporalis could help discriminate clinically prevalent TTH versus prevalent TMD. sEMG confirms to be an accurate tool to reliably objectify the subjective perception of pain. When combined with clinical evaluation and patients' symptoms, sEMG increases diagnostic sensitivity in the field of myo-type craniofacial pain disorders. This trial is registered with NCT02789085.

Conflict of interest statement

The authors declare that they have no conflicts of interest.

Copyright © 2019 Davide Pietropaoli et al.

Figures

Figure 1

(a) Density plot for sEMG (mVolts) and pain (scale 0–3) at the level of right anterior temporalis (RAT), left anterior temporalis (LAT), right masseter muscle (RMM), and left masseter muscle (LMM). (b) Overall moderate correlation between muscle tenderness and sEMG values (y = 1 + 1.2x; r2 = 0.62; p < 0.0001). Segregation of data occurs according to tenderness and sEMG values, with lower pain scores (0-1) associated with lower sEMG values (<2 mV) and higher pain scores (2-3) associated with higher sEMG values (>2 mV).

Figure 2

(a). Moderate correlation between electric values and palpation-induced pain of temporalis (y = 0.93 + 1.3x; r2 = 0.695; p < 0.0001) and masseters (y = 1.1 + 1.1x; r2 = 0.514; p=0.0062). At the highest pain score (=3), the mean sEMG absolute value (expressed in mV ± SD) is significantly higher at the ATs compared to the MMs (5.16 ± 0.47 mV vs 4.73 ± 0.30 mV, respectively; p < 0.001). (b) Pearson's analysis of single muscle sEMG findings and tenderness: strong correlation for RAT (y = 0.54 + 1.4x; r2 = 0.776; p < 0.0001); moderate correlation for LAT (y = 1.3 + 1.2 · x; r2 = 0.644; p=0.0011); moderate-low correlation for RMM (y = 1.3 + 0.96·x; r2 = 0.431; p=0.0032); moderate correlation for LMM (y = 0.81 + 1.2 · x; r2 = 0.581—p=0.0043).

Figure 3

Hierarchical cluster analysis. Single muscle tenderness and relative muscles were paired by the Euclidean correlation (columns).