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

Truini, A.a,b,*; Galeotti, F.a; Pennisi, E.a; Casa, F.a; Biasiotta, A.a; Cruccu, G.a

doi: 10.1016/j.pain.2007.01.030
Research papers
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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.

aDepartment of Neurological Sciences, “La Sapienza” University, Viale Università 30, 00185 Rome, Italy

bDepartment of Neurological, Motor and Sensorial Sciences, IRCCS San Raffaele, Via della Pisana 235, 00163 Rome, Italy

*Corresponding author. Tel.: +39 06 49919196; fax: +39 06 49919758.

E-mail: andrea.truini@uniroma1.it

Submitted June 21, 2006; received in revised form January 19, 2007; accepted January 29, 2007.

© 2007 Lippincott Williams & Wilkins, Inc.
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