10. Electrically elicited corneal reflex in primary headache

In the past vascular factors were considered pre-eminent in primary headache and, in particular, in migraine and cluster headache. More recently, an involvement of spinal trigeminal nucleus and/or brain stem nuclei modulating the transmission of nociceptive messages has been postulated. An interesting tool for exploring the trigeminal pain system is represented by the electrically elicited corneal reflex. Electrical stimulation was delivered with a thin cotton thread emerging from the end of a glass pipette filled with gauze soaked in saline solution and connected to the cathode of a constant-current stimulator. A pulse of 1 msec duration was delivered randomly (8-40 sec.). Intensity (mA) was measured by an ampmeter. The muscular response was recorded from orbicularis oculi with a surface electrode placed on the inferior lid on both sides, while the common reference electrode was on the glabella. The blink reflex was recorded using an electro-myographic device. The following electrophysiological parameters were measured: (a) latency (msec); (b) amplitude (uV); (c) duration (msec). The subjects were also asked to report subjective thresholds for tactile perception (Ttp) and pain (Tp). Using this method, we studied 21 patients suffering from Cluster Headache (CH) and 42 migraine without aura (MA) patients (IMS criteria). In the CH group a significant reduction of pain thresholds (more evident on the pain side) was observed during the active phase, while normal values were recorded during the remission phase. Ten out of 15 patients in the active phase showed a significantly reduced corneal pain threshold on the painful side. In migraine patients a significant reduction of pain threshold was observed bilaterally. Latency, amplitude and duration were normal in all the groups. The results agree with the hypothesis that an impairment of several integrative functions, including the activity of trigeminal pain control system, exists in cluster headache and migraine.