Trigeminal autonomic cephalgias (TACs).

The concept of a group of headaches whose pathophysiological focus revolves around the trigeminal-autonomic reflex fills a useful gap in characterising a number of primary headache syndromes. Broadly, these syndromes involve activation of trigeminovascular nociceptive pathways with reflex cranial autonomic activation. Clinically, this physiology predicts pain with some combination of lacrimation, conjunctival injection, nasal congestion, or eyelid oedema. Several of the primary neurovascular headaches, notably cluster headache, paroxysmal hemicrania and short-lasting neuralgiform pain with conjunctival injection and tearing (SUNCT), seem to immediately fit this classification. This physiology also explains why some patients with migraine present cranial autonomic features, and the concept is thus broadly useful for clinicians seeking a pathophysiological understanding of the primary neurovascular headaches. Given the known pathophysiology one can place the various treatments aimed at preventing these headaches or indeed treating the acute attacks, into context.