Effects of Experimental Pain and Lidocaine on Mechanical Somatosensory Profile and Face Perception

Aims: To assess the effects of experimental muscle pain and topical lidocaine applied to the skin overlying the masseter muscle on the mechanical somatosensory profile and face perception of the masseter muscle in healthy participants. Methods: A total of 28 healthy participants received a 45-minute application of a lidocaine or placebo patch to the skin overlying the masseter muscle followed by one injection of 0.2 mL sterile solution of monosodium glutamate. Measurements were taken four times during each session of quantitative sensory testing (QST) (T0 = baseline, T1 = 45 minutes after patch application, T2 = immediately after glutamate injection, and T3 = 25 minutes after the glutamate injection), and the following variables were measured: mechanical detection threshold (MDT), mechanical pain threshold (MPT), pressure pain threshold (PPT), pain report (pain on palpation, pain spreading on palpation, and pain intensity), pain drawing, and perceptual distortion. Multi-way within-subjects analysis of variance (ANOVA) was applied to the data. Results: The highest MDTs were present at T2 (F = 49.28, P .001), the lowest PPTs were present at T2 and T3 (F = 21.78, P .001), and the largest magnitude and area of perceptual distortion were reported at T2 (F > 6.48, P .001). Conclusion: Short-lasting experimental muscle pain was capable of causing loss of tactile sensitivity as well as perceptual distortion of the face, regardless of preconditioning with a topical lidocaine patch. Short-term application of a lidocaine patch did not significantly affect the mechanical somatosensory profile. Keywords: local anesthesia, musculoskeletal pain, pain measurement, sensory thresholds, touch perception