Background
Cluster headache (CH), also known as histamine headache, is a primary neurovascular headache disorder, the pathophysiology and etiology of which are not well understood. As the name suggests, CH involves a grouping of headaches, usually over a period of several weeks. According to the diagnostic criteria developed by the International Headache Society (IHS), CH has the following characteristics:
- The patient experiences attacks of severe or very severe, strictly unilateral pain (orbital, supraorbital, or temporal pain) that last 15-180 minutes and occur from once every other day to 8 times a day
- The attacks are associated with 1 or more of the following (all ipsilateral): conjunctival injection, lacrimation, nasal congestion, rhinorrhea, forehead and facial sweating, miosis, ptosis, or eyelid edema
CH may be usefully classified into 2 main forms as follows:
- Episodic CH, in which at least 2 cluster phases lasting 7 days to 1 year are separated by a cluster-free interval of 1 month or longer
- Chronic CH, in which the clusters occur more than once a year without remission or the cluster-free interval is shorter than 1 month
