Cluster Headaches

The term "cluster headache" refers to a type of headache that recurs over a period of time. People who have cluster headaches experience an episode one to three times per day during a period of time (the cluster period), which may last from two weeks to three months. People who suffer from cluster headaches get them at the same time each year, such as the spring or fall.

A cluster headache typically awakens a person from sleep one to two hours after going to bed. These nocturnal attacks can be more severe than the daytime attacks. Attacks appear to be linked to the circadian rhythm (or "biological" clock). Cluster headaches can be more intense than a migraine attack.

The headaches may disappear completely (go into "remission") for months or years, only to recur.

Cluster headaches are the least common type of headaches, affecting less than one in 1,000 people. Cluster headaches typically start before the age of 30. They are more common in men than women.

The cause of cluster headaches is unknown. However, the headaches occur when a nerve pathway in the base of the brain (the trigeminal-autonomic reflex pathway) is activated. The trigeminal nerve is the main nerve of the face responsible for sensations (such as heat or pain.)

When activated, the trigeminal nerve causes the eye pain associated with cluster headaches. The trigeminal nerve also stimulates another group of nerves that causes the eye tearing and redness, nasal congestion, and discharge associated with cluster attacks.

The activation of the trigeminal nerve appears to come from a deeper part of the brain called the hypothalamus. The hypothalamus is home to our "internal biologic clock," which regulates our sleep and wake cycles on a 24-hour schedule. Recent imaging studies have shown activation or stimulation of the hypothalamus during a cluster attack.

Cluster headaches are not caused by an underlying brain condition such as a tumor or aneurysm.

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Source: MedicineNet.com
http://www.medicinenet.com/cluster_headaches/article.htm