In the present study, we examined clinical and laser-evoked potentials (LEP) features in a group of chronic tension-type headache (CTTH) patients, in order to perform a topographic analysis of Laser evoked potentials (LEPs) and a correlation with clinical features. Eighteen patients suffering from CTTH [Headache Classification Subcommittee of the International Headache Society. The International Classification of Headache Disorders 2nd ed. Cephalalgia 2004; 24 Suppl 1, 1–159.] participated in the study. Twelve age- and sex-matched controls were also examined. We performed a basal evaluation of clinical features, Total Tenderness Score (TTS) and a topographic analysis of LEPs obtained by the hand and the pericranial points stimulation in all patients vs healthy subjects. The later LEPs, especially the P2 component, were significantly increased in amplitude in the CTTH group, specially when the pericranial points were stimulated.
The P2 wave amplitude was correlated with TTS levels and anxiety scores.
The results of this study confirm that pericranial tenderness is a phenomenon initiating a self-sustaining circuit, involving central sensitization at the level of the cortical nociceptive areas devoted to attentional and emotional components of pain.
Although tension-type headache (TTH) is the most common type of primary headache, its pathophysiology is poorly understood. The best documented abnormality in patients with TTH is increased pericranial myofascial tenderness (Vandenheede and Schoenen, 2002 and Jensen, 2003). With manual palpation of head and neck muscles, increased pericranial tenderness was found in patients with both episodic and chronic TTH (CTTH). It was demonstrated that the pericranial tenderness was positively associated with both the intensity and the frequency of tension-type headache (Bendtsen, 2000 and Jensen et al., 1993). It is generally accepted that myofascial tenderness probably plays a key role in the pathophysiology of tension-type headache. The search for peripheral mechanisms responsible for sensitization of myofascial nociceptors has however largely been unsuccessful, and muscle contraction appears to be a consequence of myofascial pain rather than a causal factor (Bendtsen, 2000). Recently, a pathophysiological model for tension-type headache was proposed. According to this hypothesis, the main problem is central sensitization at the level of the spinal dorsal horn/trigeminal nucleus, resulting from prolonged nociceptive inputs from pericranial myofascial tissues. This central sensitization is posited to cause supraspinal sensitization and central neuroplastic changes, possibly leading to increased pericranial muscle activity (Bendtsen, 2000). In a recent study we examined features of laser evoked potentials (LEPs) (Bromm and Treede, 1984 and Bromm and Treede, 1991), as well as cutaneous heat–pain thresholds to laser stimulation, in relation to the tenderness of pericranial muscles in chronic tension-type headache (CTTH), during a pain-free phase (de Tommaso et al., 2003). The amplitude of the N2–P2 complex elicited by stimulation of the pericranial zone was greater in CTTH patients than in controls; the amplitude increase was significantly associated with the Total Tenderness Score (TTS, Langermark and Olesen, 1987). Our findings suggested that pericranial tenderness may be a primary phenomenon that precedes headache, mediated by increased pain awareness at the cortical level. In that study, LEPs were examined by a derivation on the vertex to record the greatest waves. Multichannel recording of LEPs allows the performance of a topographic analysis, and the examination of all the LEP components (Valeriani et al., 2000), the earlier originating from the suprasylvian region (parietal operculum, SII), (Garcia-Larrea et al., 2003) mainly devoted to the discriminative component of pain, (Iannettia et al., 2005) and the later from the anterior cingulate cortex (ACC), (Garcia-Larrea et al., 2003) subtending the attentive and emotive features of pain (Peyron et al., 2000).
The aim of the present study was to extend previous analysis of LEPs in chronic tension-type headache, by performing multichannel topographic analysis in a new headache patients series during the pain-free phase in comparison to a group of normal subjects, and correlating the LEP findings with the Total Tenderness Score, the main clinical features, and the levels of anxiety and depression scored by the Zung, 1965 and Zung et al., 1976 scales.
