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 but fortunately do not last as long as a migraine headache.
The headaches may disappear completely (go into "remission") for months or years, only to recur without any warning.
Who Gets Cluster Headaches?
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.
What Causes Cluster Headaches?
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.
What Triggers Cluster Headaches?
The season is the most common trigger for cluster headaches, which often occur in the spring or autumn. Due to their seasonal nature, cluster headaches are often mistakenly associated with allergies or business stress. The seasonal nature of cluster headaches most likely results from stimulation or activation of the hypothalamus (see above).
Cluster headaches are also common in people who smoke and drink alcohol excessively. During a cluster period, the sufferer is more sensitive to the action of alcohol and nicotine, and minimal amounts of alcohol can trigger the headaches. During headache-free periods, the person can consume alcohol without provoking a headache.