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

• Published in: Pain (Amsterdam) Vol. 132; no. 1; pp. 102 - 107
• Main Authors: Truini, A., Galeotti, F., Pennisi, E., Casa, F., Biasiotta, A., Cruccu, G.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.11.2007; Elsevier
• Subjects: Adult; Aged; Aged, 80 and over; Biological and medical sciences; Contact heat evoked potentials; Cranial nerves. Spinal roots. Peripheral nerves. Autonomic nervous system. Gustation. Olfaction; Diagnostic Techniques, Neurological; Evoked Potentials, Somatosensory; Facial Pain - diagnosis; Facial Pain - physiopathology; Female; Fundamental and applied biological sciences. Psychology; Hot Temperature; Humans; Laser evoked potentials; Male; Medical sciences; Middle Aged; Nerve Fibers; Nervous system (semeiology, syndromes); Neurology; Neuropathic pain; Reaction Time; Somesthesis and somesthetic pathways (proprioception, exteroception, nociception); interoception; electrolocation. Sensory receptors; Trigeminal Nerve - physiopathology; Trigeminal nociceptive pathways; Trigeminal pain; Vertebrates: nervous system and sense organs; Trigeminal pain; Laser evoked potentials; Trigeminal nociceptive pathways; Contact heat evoked potentials; Neuropathic pain; Human; Reflex; Nervous system diseases; Masseter muscle; Electrophysiology; Orbicularis oculi muscle; Silent period; Peripheral neuropathy; Nerve fiber C; Nociceptor; Pain; Evoked potential; Peripheral nerve disease; Biological receptor
• ISSN: 0304-3959; 1872-6623; 1872-6623
• DOI: 10.1016/j.pain.2007.01.030

Contact heat stimuli have been reported to excite mechano-thermal nociceptors and to evoke brain potentials (CHEPs) from the limbs. We investigated whether contact heat evokes reproducible CHEPs from the trigeminal territory and may prove a reliable diagnostic tool in facial neuropathic pain. We applied contact heat stimuli to the perioral and supraorbital regions; CHEPs were recorded from the vertex in 20 controls and 2 patients with facial neuropathic pains, and reflex responses from the orbicularis oculi and masticatory muscles in 5 controls. We studied the correlation between CHEP data and perceptive ratings, site of stimulation, and age. Finally, we compared CHEPs with laser evoked potentials (LEPs). Contact heat stimuli at 51 °C evoked vertex potentials consisting of an NP complex similar to that elicited by laser pulses, though with a latency some 100-ms longer. Perioral stimulation yielded higher pain intensity ratings, shorter latency and larger amplitude CHEPs than supraorbital stimulation. CHEP data correlated significantly with age. Contact heat stimuli at 53 °C evoked a blink-like response in the relaxed orbicularis oculi muscle and a silent period in the contracted masseter muscle. In patients with facial neuropathic pain the CHEP abnormalities paralleled those seen with LEPs. We were unable to achieve reproducible signals related to C-receptor stimulation by contact heat stimuli at 41 °C in the ten subjects in whom they were tested. Contact heat stimulation, as well as laser stimulation, easily yields large-amplitude brain potentials and nociceptive reflexes, both related to the Aδ input. However CHEPs are not suitable for C-fibres potentials recording.