Trigeminal small-fibre function assessed with contact heat evoked potentials in humans.
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 degrees 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 degrees 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 degrees 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 Adelta input. However CHEPs are not suitable for C-fibres potentials recording.
Truini
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A
Department of Neurological Sciences, La Sapienza University, Viale Università 30, 00185 Rome, Italy. andrea.truini@uniroma1.it
Galeotti
F
F
Pennisi
E
E
Casa
F
F
Biasiotta
A
A
Cruccu
G
G
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003943:Diagnostic Techniques, Neurological; D005073:Evoked Potentials, Somatosensory; D005157:Facial Pain / Q000175:diagnosis* / Q000503:physiopathology*; D005260:Female; D006358:Hot Temperature; D006801:Humans; D008297:Male; D008875:Middle Aged; D009412:Nerve Fibers; D011930:Reaction Time; D014276:Trigeminal Nerve / Q000503:physiopathology*