• trigeminal autonomic cephalgias
• cluster headache
• paroxysmal hemicrania
• hemicrania continua
• SUNCT syndrome

The trigeminal autonomic cephalgias (TACs) are a group of primary headache disorders characterised by unilateral trigeminal distribution pain that occurs in association with prominent ipsilateral cranial autonomic features.¹ The group comprises cluster headache, paroxysmal hemicrania, hemicrania continua, and short lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT syndrome). Firstly, they must be differentiated from secondary TACs, and other short lasting primary headaches (table 1), and then from each other. The concept of a short lasting headache is naturally somewhat artificial in terms of defining “short”—that said, a typical attack time is less than four hours, in contrast with the major differential diagnosis of migraine in which attacks are usually longer.² The differentiation between TACs is essential since the treatments are very different. Hemicrania continua is a continuous headache and should be considered in the differential diagnosis of relatively long lasting chronic daily headache (see page ii2).³

The TACs are relatively rare, which is likely to be why they are poorly recognised in primary care. TACs will thus be referred to neurologists eventually, offering an excellent opportunity to diagnose and treat these patients. It is noteworthy that each of the TACs has been seen in paediatric practice. The importance of recognising these syndromes is underscored by their excellent but highly selective response to treatment.