Entropic Analysis of Mechanical Sensitivity in Chronic Myofascial Pain Patients

Objectives: Entropy measures can describe the dynamics and stability of various phenomena.
This study aimed to compare the entropy of masticatory muscle sensitivity between patients with chronic myofascial pain and healthy controls.
Methods: A randomized triple-blinded study included 56 male and female participants, aged 18-60, to assess the mechanical pain sensitivity of patients with chronic primary myofascial pain (n=28). A healthy control group was matched to the participants (n=28). Right and left masseter and temporalis muscles were assessed in 9 sites with 0.5, 1.0 and 2.0 kg forces (PalPeter, Sunstar-Suisse) for 2 seconds. Muscle, side, force and site were randomized for every measure. Participants rated their mechanical sensitivity using a Numerical Rating Scale from 0 (no sensation at all) to 100 (most pain imaginable), with 50 being "just barely painful". The hypothenar muscle was also assessed after facial palpation. The Entropy Score was analyzed using mechanical sensitivity of the nine sites and categorized by group, muscle, and force. Descriptive statistics and ANOVA tests were performed (sig.= 0.05); Non-overlapping 95% confidence intervals regarded significant post hoc data.
Results: Both groups reported significantly greater muscle sensitivity with greater forces applied. Myofascial Pain patients reported greater muscle sensitivity than controls with all 3 forces for all 3 muscles (p<0.03). Overall, Entropy ANOVA presented significant differences between factors (p<0.028). Post hoc tests showed that entropy was significantly higher for myofascial pain patients compared to controls when assessed with 0.5 kg for both the masseter and temporalis muscles and when assessed with 2 kg for the temporalis muscle. In addition, entropy was significantly decreased in myofascial pain patients compared to controls when assessed with 2 kg.
Conclusions: Myofascial Pain patients have higher muscle sensitivity than controls, while masseter and temporalis muscles present higher and lower entropy based on the applied force.