Trigeminal autonomic cephalalgias. Pathophysiology and classification

Trigeminal Autonomic Cephalalgias (TACs) is a grouping of headache syndromes that includes cluster headache, paroxysmal hemicrania and short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT). They are recognized clinically by their episodic, stereotypic attack profile and very often prominent cranial autonomic symptoms, such as lacrimation, conjunctival injection or rhinorrhea. They involve afferent activation of the trigeminal innervation of intracranial pain-producing structures, or the perception of that activation, and reflex activation of the facial, seventh cranial, nerve outflow pathway. This excess reflex trigeminal-autonomic activation seems to be permitted by dysfunction in the brain, specifically in the posterior hypothalamic gray matter. Understanding the anatomy and physiology of these disorders has greatly facilitated their management and the development of exciting new strategies such as neuromodulatory approaches to the management of the more intractable cases.