Heat pain thresholds and cerebral event-related potentials following painful CO2 laser stimulation in chronic tension-type headache

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Abstract
Current opinion concerning the pathophysiology of tension-type headache (TTH) and its related pericranial muscle tenderness proposes a primary role of central sensitization at the level of dorsalhorn/trigeminal nucleus as well as the supraspinal level. Investigation of these phenomena can be conducted using laser-evoked potentials (LEPs), which are objective and quantitative neurophysiological tools for the assessment of pain perception. In the present study we examined features of LEPs, as well as cutaneous heat-pain thresholds to laser stimulation, in relation to the tenderness of pericranial muscles in chronic TTH resulting from pericranial muscle disorder, during a pain-free phase. Twelve patients with TTH and 11 healthy controls were examined using the Total Tenderness Scoring (TTS) system. The stimulus was a laser pulse generated by a CO2 laser. The dorsum of the hand and the cutaneous zones corresponding to pericranial muscles were stimulated. Subjective perception of stimulus intensity was assessed by a visual analogue scale. Two responses, the earlier named N2a and the last named P2, were considered; the absolute latency was measured at the highest peak of each response. The N2a–P2 components' peak-to-peak amplitude was detected. The heat pain threshold was similar in TTH patients and controls at the level of both the hand and pericranial skin. The TTS scores at almost all pericranial sites were higher in TTH patients than in normal controls. The amplitude of the N2a–P2 complex elicited by stimulation of the pericranial zone was greater in TTH patients than in controls; the amplitude increase was significantly associated with the TTS score. Our findings suggest that pericranial tenderness may be a primary phenomenon that precedes headache, and is mediated by a greater pain-specific hypervigilance at the cortical level.