The Effect of Topical Anaesthesia on Pressure Pain Thresholds in Symptom-free Subjects

Palpation, a standard procedure in the diagnostic process of muscular pain conditions – myalgia, aims to provoke a muscular pain response. The origin of pain elicited by palpation is not fully understood. There is also a possibility that the pressure elicit response from mechanoreceptors in skin, sub mucosal tissue or periosteum, which may affect the validity of the method. The aim of this study was to evaluate the effect of topical anesthesia on pressure pain thresholds at masseter, temporal and thumb muscle sites in healthy individuals. Twenty symptom-free subjects (ten males/ ten females) mean age 24.6 years (SD 2.6) participated in this double blind randomized experimental trial. An algometer (Somedic AB) was used to measure Pressure Pain Thresholds (PPT), on the masseter, temporal and thumb before and after topical application of EMLA or a placebo cream. There was no statistically significant change in PPTs at any of the tested sites between the baseline and after application of EMLA and placebo cream. Furthermore, there was no significant difference in PPTs between sexes. There was no significant difference in PPTs between the different muscle sites, apart from a higher PPT for the thumb site compared to the masseter muscle. In conclusion, PPT was not affected by topical anaesthesia in symptom-free subjects. This indicates that palpation pain is not dermal. Furthermore did PPT not differ between the masseter and temporal muscles. The study indicates that the same palpation pressure may be used for extra-oral palpation of the temporal and masseter muscle for both sexes.