Trigeminal small-fibre function assessed with contact heat evoked potentials in humans

Area of Science:

• Neuroscience
• Pain Research
• Neurology

Background:

• Contact heat stimuli are known to activate mechano-thermal nociceptors and elicit brain potentials (CHEPs) from the limbs.
• The trigeminal territory's response to contact heat and its diagnostic potential for facial neuropathic pain remain less explored.

Purpose of the Study:

• To investigate the reproducibility of contact heat-evoked potentials (CHEPs) in the trigeminal territory.
• To assess the reliability of CHEPs as a diagnostic tool for facial neuropathic pain.
• To compare CHEPs with laser-evoked potentials (LEPs).

Main Methods:

• Contact heat stimuli were applied to the perioral and supraorbital regions in healthy controls and patients with facial neuropathic pain.
• Contact heat-evoked potentials (CHEPs) were recorded from the vertex.
• Reflex responses from orbicularis oculi and masticatory muscles were also recorded.
• Correlations between CHEP data, pain ratings, stimulation site, and age were analyzed.

Main Results:

• Contact heat stimuli (51°C) evoked vertex potentials (NP complex) with longer latency than laser pulses.
• Perioral stimulation resulted in higher pain ratings and more robust CHEPs compared to supraorbital stimulation.
• CHEPs correlated significantly with age.
• Contact heat stimuli (53°C) elicited nociceptive reflexes (orbicularis oculi response, masseter silent period).
• In patients, CHEP abnormalities mirrored those observed with LEPs.
• Reproducible C-fiber potentials were not obtained with contact heat stimuli at 41°C.

Conclusions:

• Contact heat stimulation effectively evokes brain potentials and nociceptive reflexes related to Adelta fiber input.
• CHEPs show promise as a diagnostic tool for facial neuropathic pain, with abnormalities paralleling LEPs.
• Contact heat stimulation is not suitable for recording C-fiber potentials.