Cluster headache sufferers typically experience very severe headaches of a piercing quality near one eye or temple that last for fifteen minutes to three hours. The headaches are unilateral and occasionally change sides.

Cluster headaches are frequently associated with drooping eyelids, conjunctival injection (which results in red, watery eyes), tearing, constricted pupil, eyelid edema, nasal congestion, runny nose, and sweating on the affected side of the face. The neck is often stiff or tender in association with cluster headaches, and jaw and teeth pain is sometimes reported.

The location and type of pain has been compared to a "brain-freeze" headache from rapidly drinking or eating something very cold like an ice cream; this analogy is limited, but may offer some insight into the cluster headache experience. Persons who have experienced both cluster headaches and other painful conditions (childbirth, migraines) report that the pain of cluster headaches is far worse, sometimes 100 times more severe than a migraine. One analogy is that of a burning ice pick being repeatedly stabbed through the eye into the brain.

During an attack, the person is usually restless and unable to be still and may pace or even become agitated. Sensitivity to light is more typical of a migraine, as is vomiting, but they can be present in some sufferers of cluster headache.

Cluster headaches are occasionally referred to as "alarm clock headaches", as they can occur at night and wake a person from sleep at the same time each night or at a certain period after falling asleep. Other synonyms for cluster headache include Horton's syndrome and "suicide headaches" (a reference to the excruciating pain and resulting desperation).

In episodic cluster headache, these attacks occur once or more daily, often at the same times each day, for a period of several weeks, followed by a headache-free period lasting weeks, months, or even years. Approximately 10-15% of cluster headache sufferers are chronic; they can experience multiple headaches every day for years.

Episodic or chronic

Cluster headaches occurring in two or more cluster periods lasting from 7 to 365 days with a pain-free remission of one month or longer between the clusters are considered episodic. If the attacks occur for more than a year without a pain-free remission of at least one month, the condition is considered chronic. The condition may change from chronic to episodic and from episodic to chronic. Remission periods lasting for decades before the resumption of clusters have been known to occur.

Prevalence

While migraines are diagnosed more often in women, cluster headaches are diagnosed in men at a rate 2.5 to 3 times greater than in women. This gap between the sexes has narrowed over the past few decades, and it is not clear whether cluster headaches are becoming more frequent in women, or whether they are merely being better diagnosed. Between 1 and 4 people per thousand experience cluster headaches in the U.S. and Western Europe; statistics for other parts of the world are fragmentary. Latitude plays a role in the occurrence of cluster headaches, which are more common as one moves away from the equator towards the poles. It is believed that greater changes in day length are responsible for the increase.

Pathophysiology

Gray's FIG. 778– Trigeminal nerve is shown in yellow.

Gray's FIG. 777– Detailed view of opthalmic nerve, shown in yellow.

Cluster headaches are classified as vascular headaches. The intense pain is caused by the dilation of blood vessels which creates pressure on the trigeminal nerve. While this process is the immediate cause of the pain, the etiology (underlying cause or causes) is not fully understood.

Hypothalamus

Among the most widely accepted theories is that cluster headaches are due to an abnormality in the hypothalamus. This can explain why cluster headaches frequently strike around the same time each day, and during a particular season, as one of the functions the hypothalamus performs is regulation of the biological clock and metabolic abnormalities have also been reported in patients.

The hypothalamus is responsive to light—daylength and photoperiod; olfactory stimuli, including pheromones; steroids, including sex steroids and corticosteroids, neurally transmitted information arising in particular from the heart, the stomach, and the reproductive system; autonomic inputs; blood-borne stimuli, including leptin, ghrelin, angiotensin, insulin, pituitary hormones, cytokines, blood plasma concentrations of glucose and osmolarity, etc.; and stress. These particular sensitivities may underly the causes, triggers, and methods of treatment of cluster headache.

Genetics

There is a genetic component to cluster headaches, although no single gene has been identified as the cause. First-degree relatives of sufferers are more likely to have the condition than the population at large. However, genetics appears to play a much smaller role in cluster headache than in some other types of headaches.

Triggers

Nitroglycerin (glyceryl trinitrate) can sometimes induce cluster headaches in sufferers in a manner similar to spontaneous attacks. Ingestion of alcohol is recognized as a common trigger of cluster headaches when a person is in cycle or susceptible. Exposure to hydrocarbons (petroleum solvents, perfume) is also recognized as a trigger for cluster headaches. Some patients have a decreased tolerance to heat, and becoming overheated may act as a trigger. Napping causes a headache for some sufferers. The role of diet and specific foods in triggering cluster headaches is controversial and not well understood.

Treatment

Many doctors, even neurologists, are unfamiliar with this disease, and cluster headaches often go undiagnosed for many years.

Medically, cluster headaches are considered benign, but because of the extreme and often debilitating pain associated with them, a severe attack is nevertheless treated as a medical emergency by doctors who are familiar with the condition. Doctors who are less familiar with the disease may neglect sufferers in emergency rooms and force them to endure inordinate spans of time before receiving treatment, if any treatment at all is granted. Sometimes, sufferers of the disease may even be accused of drug-seeking behavior.

Over-the-counter pain medications (such as aspirin, acetaminophen, and ibuprofen) have no effect on the pain from a cluster headache. Unlike other headaches such as migraines and tension headaches, cluster headaches do not respond to biofeedback.

Some have reported partial relief from narcotic pain killers, but the frequency of their use in a cluster cycle (1-8 or more times a day) often disqualifies them from use and they are mostly ineffective due to the intensity of the pain involved in cluster attacks. Anecdotal evidence indicates that cluster headaches can be so excruciating that even morphine does little to ease the pain. However, some newer medications like fentanyl have shown promise in early studies and use.

Medications to treat cluster headaches are classified as either abortives or prophylactics (preventatives). In addition, short-term transitional medications (such as steroids) may be used while prophylactic treatment is instituted and adjusted.

Abortive treatment

The most successful abortives include breathing pure oxygen (12-15 liters per minute in a non-rebreathing apparatus) and triptan drugs like sumatriptan and zolmitriptan. Because of the rapid onset of an attack, the triptan drugs are usually taken nasally or by subcutaneous injection rather than by mouth.

Hot showers have helped about 15% of people who try them. Other abortive remedies that work for some and not for others include ice, cold showers, breathing cold air, caffeine, and drinking large amounts of water in the early stages of an attack.

Prophylactic treatment

A wide variety of prophylactic medicines are in use, and patient response to these is highly variable. Preventatives include muscle relaxants, lithium, calcium channel blockers such as verapamil, ergot compounds, prednisolone, anti-seizure medicines, and atypical anti-psychotics.

Magnesium supplements have been shown to be of some benefit in about 40% of patients. Melatonin has also been reported to help some. Feverfew, a herb used to treat migraine, is not clearly beneficial according to anecdotes from web forums. A large proportion of those trying kudzu have reported supression of the symptoms.

There is substantial anecdotal evidence that serotonergic psychedelics such as psilocybin (mushrooms) and LSD and LSA d-Lysergic acid amide (Rivea corymbosa seeds) abort cluster periods and extend remission periods. A clinical study of these treatments under the auspices of MAPS is being developed by researchers at Harvard Medical School, McLean Hospital. Melatonin, psilocybin, serotonin, and the triptan abortive drugs are closely-related tryptamines.

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