Neurophysiology of cluster headache and other trigeminal autonomic cephalalgias

“Cluster headache and other trigeminal autonomic cephalalgias” is a category of primary headaches characterized by strictly unilateral headache with concomitant ipsilateral facial autonomic features. Their pathophysiology is not fully understood. Many neurophysiological techniques have been used in attempts to disentangle the pathophysiological mechanisms underlying these elusive brain disorders. Overall, these investigations have revealed side-to-side differences, in virtually all the sensory modalities explored (both pain-related and non-pain-related), in patients (almost always cluster headache patients) versus healthy controls. Signs of peripheral and central sensitization of the trigeminal system, as well as of the extracephalic spinal pain processing system, have been detected using blink and lower limb withdrawal reflexes in cluster headache. In some cases, acute or prophylactic treatments can reverse these dysfunctions. The use of improved selection criteria and more refined neurophysiological techniques, especially if combined with neuroimaging data, should lead to greater understanding of the nature of the brain dysfunction in trigeminal autonomic cephalalgias.