The second edition of the headache classification from the International Headache Society (IHS) has defined a new primary headache grouping named the trigemino-autonomic cephalgias (TAC).¹ All of these headache syndromes have two features in common: relatively short-lasting, unilateral, severe headache attacks, and, typically, accompanying cranial autonomic symptoms. These autonomic symptoms occur on the side of the headache and comprise lacrimation, conjunctival injection, rhinorrhea, miosis, and ptosis. The most important and prevalent of these headache disorders is cluster headache.

Cluster headache is defined as a paroxysmal, strongly unilateral, very severe headache, typically with a retro-orbital maximum of pain. The occurrence of cranial autonomic symptoms is obligatory, but can be replaced by restlessness/agitation. The attacks occur up to eight times a day, sometimes with a nocturnal preponderance, and last for between 15 and 180 minutes and, rarely, several hours. The episodic form of cluster headache occurs in 80% of cluster headache sufferers, with bouts lasting for between seven and 365 days separated by pain-freeremission periods of longer than one month’s duration. If the cluster attacks occur for longer than one year without remission periods or with remission periods lasting for less than one month, the diagnosis is chronic cluster headache. This is the case in 15–20% of cluster headache sufferers. The two forms do not necessarily evolve from one another. The lifetime prevalence of cluster headache is about 0.1%, with a mean male-to-female ratio of 4.3:1.² A genetic background for cluster headache has not been described but is likely.³ Cluster headache can be seen even in children and in very old adults.⁴ There is a familial occurrence in 2–7% of cases. On average, the headaches start at 28–30 years of age, but they can start at any age; after 15 years, 80% of cluster headache patients still have attacks.⁵

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