What are cluster headaches?
Cluster headache is a well-defined, rare, but often misdiagnosed syndrome characterized by excruciatingly severe unilateral headaches that last from a half hour to three hours, with an average duration of forty-five minutes. Its features include paroxysmal onset of one side of the head, a short duration, and episodic occurrence. The pain often wakes sufferers one to two hours after they fall asleep. “Cluster” refers to the original perception that the headaches emerged in groups over a period of time (called the cluster period) lasting weeks to months, followed by periods that are free of pain and attacks (called remission or interim periods). The International Headache Society divides cluster headaches into episodic cluster and chronic cluster, with chronic further subclassified into primary and secondary variants. Chronic cluster headaches do not have a cessation, or interim, period but recur for years.
The precise cause of cluster headaches is unknown, although the season of the year is the most common trigger. Because they usually begin with spring or autumn, cluster headaches are often misattributed to seasonal allergies (such as hay fever) or seasonal-related stress (such as the beginning of school, final examinations, or the height of business cycles).
Positron emission tomography (PET) scanning has revealed that in cluster headaches the hypothalamus activates the trigeminal nerve, which is responsible for most of the severe pain. Located deep in the brain, the hypothalamus is also responsible for the internal biological clock that regulates the approximately twenty-four-hour sleep-wake cycle. The production and activity of the neurotransmitter serotonin, which is important in the self-regulation of these circadian rhythms, is also altered during attacks. Cluster headache is not related to the development of tumors or lesions.
Cluster headaches are rare. No more than .03 percent of the population ever experiences them. Men suffer them more than women do, although with improvements in epidemiological techniques the known ratio has been changed from 7:1 to 2:1. The age of onset is usually in the late twenties. As with migraine headaches, cluster headaches tend to run in families, with a fourteenfold increase in the chances of having them if a first-degree relative (mother, father, son, daughter, brother, or sister) suffers from the syndrome. In addition, a statistically significant incidence of migraine headaches exists in families with a cluster headache sufferer.
Cluster headache attacks, which are excruciatingly severe, debilitating, and dramatic, are almost always unilateral and occur from one to six times a day. They are most intense in, around, or behind one eye. Because the pain, commonly described as “boring” or “stabbing,” often spreads into the upper teeth, jaw, neck, or temple, the headaches can be misdiagnosed as coming from dental or sinus problems. The attacks are rapid, peaking in five to ten minutes, and are occasionally, but not frequently, preceded by a visual aura. Attacks are much more likely to occur if tobacco and/or alcohol have been recently used, and they even more frequently will awaken sufferers during their first hour of napping or sleeping.
While migraine headache sufferers seek quiet, darkened places and try to remain still, cluster headache sufferers feel more pain if they try to lie down or recline in a chair. Typically, cluster headache sufferers are restless, pacing back and forth, or want to sit upright, holding their heads with their hands. A sufferer may even bang his or her head against a wall to obtain relief.
Treatments are oriented either toward abortive therapies or prophylactic therapies. Abortive approaches attempt to shorten the duration and/or intensity of an individual attack. Prophylactic approaches attempt to shorten or prevent the cluster periods themselves. While a fortunate characteristic of the attacks is their brevity, this feature also limits the range of abortive measures that can be undertaken; by the time that some agents are metabolized, the attack is over.
Although not always practical, a successful and safe abortive treatment is simply breathing 100 percent oxygen for ten to twenty minutes through a nonrebreathing mask. Also not always practical but effective are subcutaneous injections of sumatriptan (Imitrex) or intravenous, intramuscular, or subcutaneous injections of dihydroergotamine (Migranal). Other effective first-line therapies for acute intervention include zolmitriptan (Zomig) tablets, intranasal lidocane, or ergotamine (Cafergot).
Prophylactic, or preventive, treatments prevent attacks or at least lessen their intensity. All cluster headache sufferers should be on a prophylactic regimen (unless their cluster periods are less than two weeks, which is rarely the case). Verapamil (marketed as Calan, Covera, Isoptin, Tarka, and Verelan) is the most commonly prescribed medication because its mechanism as a calcium-channel blocker is well understood and it is usually effective. Occasionally, higher-than-typical doses must be employed. For those who do not respond well or receive sufficient relief on verapamil alone, a second medication such as ergotamine, lithium, methysergide (Sansert), or prednisone is often added. Sometimes, these second medications are effectively used alone, as are valproic acid and divalproex (Depakote).
In the event that pharmacology proves ineffective, several surgical or radiation techniques can block the trigeminal-autonomic reflex pathway. The benefits of these, or any, invasive treatments must be weighed against potential harm. For example, corneal anesthesia, needed to carry out these procedures, can put the eye at risk.
People have suffered from cluster headaches as long as people have suffered from headaches, although the rarity, seasonal occurrence, and symptoms of cluster headaches have made their recognition as a distinct syndrome difficult. Through PET scanning, neurovascular research has identified three areas of the brain particularly affected by cluster headaches. Because two of these areas are affected every time any sort of pain is felt, research is being concentrated on the third area, hypothalamic gray matter. Researchers expect that probes here will resolve their biggest debate: Is the vasodilation associated with cluster headache the primary problem or the result of activation of the trigeminal vascular system? Researchers do agree that cluster headaches, while distinct, belong to a family of related conditions, the cranial neuralgias.
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