Central Mechanisms of Amplification in Chronic Orofacial Myofascial Pain: Analysis of Experimental Modulation of Somatosensory Sensitivity and the Nociceptive Blink Reflex.

• Grant number: 25/10791-2
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)
• Start date: November 01, 2025
• End date: February 28, 2029
• Field of knowledge: Biological Sciences - Physiology
• Principal Investigator: Yuri Martins Costa
• Grantee: Isadora Alves Lorenzo
• Host Institution: Faculdade de Odontologia de Piracicaba (FOP). Universidade Estadual de Campinas (UNICAMP). Piracicaba , SP, Brazil
• Associated research grant: 19/15826-8 - Central mechanisms of pain amplification in patients with chronic myofascial orofacial pain: exploring new potentialities of somatosensory and neurophysiological assessment, AP.JP

Abstract

This study aims to evaluate the effect of secondary hyperalgesia induced by capsaicin and local anesthesia on the modulation of the somatosensory profile and the excitability of trigeminal nociceptive pathways in patients with chronic orofacial myofascial pain and healthy volunteers. Patients with chronic orofacial myofascial pain (n=78) and a sample of healthy controls (n=33) will be assessed. This double-blind, randomized, placebo- controlled experimental study will be conducted through consecutive experimental sessions separated by 24 hours. The sessions will involve sensory modulation using local anesthesia and topical capsaicin. In the sessions involving local anesthesia, participants will receive a 30-minute application of 4% lidocaine cream or a placebo cream to the skin overlying the most painful masseter (for patients) or the right masseter (for controls), as well as to the ipsilateral forearm. These sessions will occur under two different conditions: with the administration of 2 ml of 2% lidocaine or with no injection. In the sessions involving topical capsaicin, participants will receive a 45-minute application of 1% capsaicin to the same aforementioned sites. In addition to somatosensory testing, the nociceptive blink reflex will be evaluated in the infraorbital nerve output region, and conditioned pain modulation will be assessed during the baseline session. The analyses will primarily focus on identifying subgroups of patients with chronic orofacial myofascial pain based on their modulatory response to local anesthesia and capsaicin in the neurophysiological profile, using the absolute differences in Z-scores between the lidocaine, placebo, and capsaicin sessions compared to baseline sessions.