Cervical referral of head pain in migraineurs: effects on the nociceptive blink reflex.

OBJECTIVE To investigate cervical, interictal reproduction of usual head pain and its effect on the nociceptive blink reflex in migraineurs. BACKGROUND Anatomical and neurophysiological studies in animals and humans have confirmed functional convergence of trigeminal and cervical afferent pathways. Migraineurs often present with occipital and neck symptoms, and cervical pain is referred to the head in most cases, suggesting that cervical afferent information may contribute to headache. Furthermore, the effectiveness of greater occipital nerve blockade in migraine and demonstrable modulation of trigeminal transmission following greater occipital nerve blockade suggest an important role for cervical afferents in migraine. However, to what extent cervical afferents contribute actively to migraine is still unknown. METHODS The passive accessory intervertebral movements of the atlanto-occipital and C2-3 spinal segments of 15 participants (14 females, 1 male; age 24-44 years, mean age 33.3 years) with migraine were examined interictally. During 1 session, either the atlanto-occipital or C2-3 segment was examined, resulting in referred usual head pain, while in another session, pressure was applied over the common extensor origin (lateral epicondyle of the humerus) of the ipsilateral arm. Each intervention was repeated 4 times. The nociceptive blink reflex to a supraorbital electrical stimulus was elicited ipsilaterally during both sessions before and during each intervention. The main outcome variables were the number of recorded blinks, area under the curve and latencies of the R2 components of the nociceptive blink reflex. Participants also rated the intensity of referred head pain and the supraorbital stimulus on a scale of 0-10, where 0 = "no pain" and 10 = "intolerable pain," and rated the intensity of applied pressure where 0 = "pressure but no pain" and 10 = "intolerable pain." RESULTS Participants reported a significant reduction in local tenderness ratings across the 4 trials for the cervical intervention but not for the arm (P = .005). The cervical intervention evoked head pain in all participants. As the cervical intervention was sustained, head pain decreased significantly from the beginning to the end of each trial (P = .000) and from the beginning of the first trial to the end of the last (P = .000). Pain evoked by the supraorbital stimulus was consistent from baseline to across the 4 trials (P = .635) and was similar for the cervical and arm interventions (P = .072). The number of blinks decreased significantly across the experiment (P = .000) and was comparable in the cervical and arm interventions (P = .624). While the R2 area under the curve decreased irrespective of intervention (P = .000), this reduction was significantly greater for the cervical intervention than when pressure was applied to the arm (P = .037). Analysis of the R2 latencies revealed a notable increase across the experiment (P = .037). However, this increase was significantly greater following the cervical than arm intervention (P = .012). CONCLUSIONS Our findings corroborate previous results related to anatomical and functional convergence of trigeminal and cervical afferent pathways in animals and humans, and suggest that manual cervical modulation of this pathway is of potential benefit in migraine.