RELATED STORIES • Common headache types PAIN MANAGEMENT Headache • Migraine headache • Tension headache • Cluster headache • Rebound headaches • Primary cough headaches • Ice cream headaches • Exercise headaches • External compression headaches • Spinal headaches • Thunderclap headaches • Sex headaches • Chronic daily headaches • Sinus headaches

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In most cases headache pain, even severe headache pain, isn't the result of any underlying disease. In fact, the vast majority of headaches are primary headaches — headaches that aren't caused by a specific medical condition. These include migraines, tension-type headaches and cluster headaches.

Cluster headache is distinctive in ways other than the severity of the pain. A striking feature of cluster headache is that the attacks occur in cyclical patterns, or clusters — which gives the condition its name. Bouts of frequent attacks, in what's known as cluster periods, may last from weeks to months, followed by remission periods when the headache attacks stop completely. Although the pattern varies from one person to another, most people have one or two cluster periods a year. During remission, no headaches occur for months, and sometimes even years.

Cluster headache is one of the most painful types of headache. Fortunately, cluster headache is rare, affecting less than 1 percent of the U.S. population. The condition is more common in men. Cluster headache can affect people at any age but is most common between adolescence and middle age.

Although cluster headache attacks are extremely painful, they're not life-threatening. Several treatments are available to help make the attacks shorter and less severe. In addition, preventive medications can help reduce the number of headaches.

A cluster headache strikes quickly, usually without warning. Within minutes, excruciating pain develops. The pain typically develops on the same side of the head throughout a cluster period, and often the headaches remain on that side throughout a person's life. Less frequently, the pain may switch to the opposite side of the head in the next cluster period. Rarely, the pain switches sides from one attack to another.

The pain of a cluster headache is often described as sharp, penetrating or burning. People with this condition say that the pain feels like a hot poker being stuck in the eye or that the eye is being pushed out of its socket.

Restlessness
People with cluster headache appear restless, preferring to pace or sit and rock back and forth to soothe the attack. They may press a hand against the eye or scalp or apply ice or heat over the painful area. In contrast to people with migraine, people with cluster headache usually avoid lying down during an attack because this position seems to only increase the pain.

Most people with a cluster headache prefer to be alone. They may remain outdoors, even in freezing weather, for the duration of an attack. They may scream, bang their heads against a wall or hurt themselves in some way as a distraction from the unbearable pain. Some may find relief by exercising, such as jogging in place or doing sit-ups or push-ups.

If cluster headache attacks regularly occur at night, some people try to remain awake for as long as possible to forestall the onset of a headache they know is coming. Unfortunately, doing so only speeds up the sleep cycle. The headache may occur within minutes of falling asleep in a compressed sleep cycle. In the worst cases, a vicious cycle of head pain and sleep deprivation develops. This can lead to depression and thoughts of suicide.

Teary eye and stuffed nose
Cluster headache always triggers a response from the autonomic nervous system. This system controls many vital activities without your consciously having to think about them. For example, your autonomic nervous system regulates blood pressure, heartbeat, sweating and body temperature. The most common autonomic response to a cluster headache is excessive tearing and redness of the eye on the side of the head affected by the pain.

Other signs and symptoms that may accompany cluster headache include:

• Stuffy or runny nasal passage in the nostril on the affected side of the face
• Red, flushed face
• Swelling around the eye on the affected side of the face
• Reduced pupil size
• Drooping eyelid

Most of the time, these signs and symptoms last only as long as the headache lasts. In some people, however, a drooping eyelid and reduced pupil size persist after long periods of attacks. Some migraine-like symptoms, including nausea, sensitivity to light and sound, and aura, may occur with a cluster headache.

Cluster period characteristics
A cluster period generally lasts from two to 12 weeks. Chronic cluster periods may continue for more than a year. The starting date and the duration of each cluster period often are amazingly consistent from period to period. For many people, cluster periods occur seasonally, such as every spring or every fall. It's common for clusters to begin soon after one of the solstices — the longest and shortest days of the year. Over time, cluster periods may become more frequent, less predictable and longer lasting.

During a cluster period, headaches typically occur every day, sometimes several times a day. A single attack lasts 45 to 90 minutes on average. The attacks happen often at the same time within each 24-hour day. Nighttime attacks are more frequent than daytime attacks, often occurring 90 minutes to three hours after you fall asleep. The most common times for attacks are between 1 a.m. and 2 a.m., between 1 p.m. and 3 p.m., and around 9 p.m.

Cluster headache can be frightening to the person affected by it and to his or her family and friends. The debilitating attacks may seem unbearable. But the pain usually ends as suddenly as it begins, with rapidly decreasing intensity. After attacks, most people are completely free from pain but exhausted. Temporary relief during a cluster period may be only a matter of hours or may last as long as a day before the next attack.

Based on the length of the cluster periods and the remission periods, the International Headache Society has classified cluster headache into two types:

• Episodic. In this form, cluster headache occurs daily for one week to one year, followed by a pain-free remission period lasting weeks to years before another cluster period develops.
• Chronic. In this form, cluster headache occurs daily for more than a year with no remission or with pain-free periods lasting less than two weeks.

About 10 percent to 20 percent of people with cluster headache have the chronic type. Chronic cluster headache may develop after a period of episodic attacks, or it may develop spontaneously, without a prior history of headaches. Some people experience alternating episodic and chronic phases.

Researchers point to different mechanisms to explain the major characteristics of cluster headache. There may be a family history of cluster headache in some people with this condition, meaning a possible genetic component. Several factors may work together to produce cluster headache.

Cluster headache triggers
Unlike migraine and tension-type headache, cluster headache generally isn't associated with triggers such as foods, hormonal changes or stress. But some people with cluster headache are heavy drinkers and cigarette smokers. Once a cluster period begins, consumption of alcohol can trigger a splitting headache within minutes. All it takes is one drink. For this reason, many people with cluster headache stay completely away from alcohol for the duration of a cluster period. Other possible triggers include the use of medications such as nitroglycerin, a drug used to treat heart disease.

The beginning of a cluster period often follows occasions when normal sleep patterns are disrupted, such as during a vacation or when starting a new job or work shift. Some people with cluster headache also have sleep apnea, a condition in which the walls of a person's throat collapse momentarily, obstructing the sleeper's breathing repeatedly during the night.

Increased sensitivity of nerve pathways
The intense pain of a cluster headache is centered behind or around the eye, an area that's served by the trigeminal nerve, a major pathway for pain. Stimulation of this nerve results in abnormal reactions of the arteries that supply blood to the head. These blood vessels dilate and become painful.

Some symptoms of cluster headache, such as teary eye, stuffy or runny nose and droopy eyelid, involve the autonomic nervous system. The nerves that are part of this system form a pathway at the base of the brain. When the trigeminal nerve is activated, causing eye pain, autonomic nerves are also activated in what is called the trigeminal-autonomic reflex. Researchers believe that a still unidentified process involving inflammation or abnormal blood vessel activity in this region may also be involved in the headache.

Abnormal function of the hypothalamus
Cluster attacks typically occur with clock-like regularity during a 24-hour day. The cycle of cluster periods often follow the seasons of the year. These patterns suggest that the body's biological clock is involved. In humans, the biological clock is located in the hypothalamus, which lies deep in the center of the brain. Among the many functions of the hypothalamus is control of the sleep-wake cycle and other internal rhythms.

Abnormalities of the hypothalamus may explain the timing and cyclical nature of cluster headache. Studies have detected increased activity in the hypothalamus during the course of a cluster headache. This activity isn't seen in people with other headaches such as migraine.

Studies also indicate that people have abnormal levels of certain hormones, including melatonin and testosterone, during cluster periods. These hormonal changes are believed to be due to a problem with the hypothalamus. Other studies reveal that participants with cluster headache have a larger hypothalamus, compared with that of participants who don't have this headache. But it remains unknown what causes these abnormalities in the first place.

Unlike migraine, which more often affects women, cluster headache predominantly affects men. Eighty-five percent of people affected by cluster headache are men between the ages of 20 and 50. Many people who get cluster headache attacks are heavy smokers. Alcohol can trigger an attack if you're at risk of cluster headache. Usually there's no family history of cluster headache.

Headache pain, even when severe, usually isn't the result of an underlying disease. Occasionally, however, headaches may indicate a serious underlying medical condition, such as a brain tumor or rupture of a weakened blood vessel (aneurysm). Be sure to tell your doctor about any headache that concerns you. If you have a history of headaches, see your doctor if the pattern changes or your headaches suddenly feel different.

In addition, see your doctor or go to the emergency room immediately if you have any of these signs and symptoms:

• Abrupt, severe headache, often like a thunderclap
• Headache with a fever, stiff neck, rash, mental confusion, seizures, double vision, weakness, numbness or speaking difficulties, which may indicate a number of problems, including stroke, meningitis, encephalitis or brain tumor
• Headache after a head injury, even if it's a minor fall or bump, especially if it gets worse
• Chronic, progressive headache that worsens after coughing, exertion, straining or a sudden movement
• Onset of new headache pain after age 40

Call your doctor if your child has head pain that's severe or that causes him or her to miss school or other activities. Children who are too young to tell you what's wrong may cry and hold their heads to indicate severe pain.

Cluster headache has a characteristic type of pain and pattern of attacks. A diagnosis depends on your description of the attacks, including your pain, the location and severity of your headaches, and associated symptoms. The frequency and duration of your headaches also are important factors.

If you have chronic or recurrent headaches, your doctor may try to pinpoint the type and cause of your headache using certain approaches.

Examinations and tests

• Neurological examination. A neurological examination may help your doctor detect physical signs of a cluster headache. Sometimes the pupil of your eye may appear smaller or your eyelid may droop, even between attacks.
• Imaging tests. If you have unusual or complicated headaches or an abnormal neurological exam, you may undergo other diagnostic testing to rule out other serious causes of head pain, such as a tumor or aneurysm. Two common brain-imaging tests are computerized tomography (CT) and magnetic resonance imaging (MRI) scans. A CT scan uses a series of computer-directed X-rays to provide a comprehensive view of your brain. An MRI doesn't use X-rays. Instead, it combines magnetism, radio waves and computer technology to produce clear images of your brain.

Headache tracking
One of the most helpful things you can do is keep a headache journal for at least two months. Each time you get a headache, jot down the following information:

• A description of the pain
• The severity of the pain
• The location of the pain
• The duration of the pain
• Any medications you're taking

A headache journal can offer valuable clues that may help your doctor diagnose your particular kind of headache and discover possible headache triggers.

There's no cure for cluster headaches. The goal of treatment is to help decrease the severity of pain and shorten the headache period.

Acute medication
The purpose of acute treatment is to stop or reduce pain after a cluster headache starts. Because the headache peaks quickly, acute medications must be fast-acting and delivered quickly, using an injection or inhaler rather than oral tablets. You must be ready to take the medication as soon as an attack starts. And you may want to teach family members about your medications so that they'll be able to help you when you have an attack.

Because the pain of a cluster headache comes on suddenly and may subside within a short time, over-the-counter pain relievers such as aspirin or ibuprofen (Advil, Motrin, others) aren't effective. The headache is usually gone before the drug starts working. Fortunately, other types of acute medication can provide some pain relief. Treatment of cluster headache is focused more on prevention, with more medication options available to choose from.

Acute treatments include:

• Oxygen. Briefly inhaling 100 percent oxygen through a mask at a rate of 7 liters per minute provides dramatic relief for about 50 to 90 percent of people who use it. Occasionally, a higher flow rate may be more effective. The effects of this safe, inexpensive procedure can be felt within 15 minutes. The major drawback of oxygen is the need to carry an oxygen cylinder and regulator with you, which can make the treatment inconvenient and inaccessible at times. Small, portable units are available, but some people still find them impractical. Sometimes, oxygen may only delay rather than stop the attack, and pain may return.
• Sumatriptan. The injectable form of sumatriptan (Imitrex), which is commonly used to treat migraine, is also an effective acute treatment for cluster headache. Some people may benefit from using sumatriptan in nasal spray form, but more studies are needed to determine the effectiveness of this approach. Sumatriptan isn't recommended for people with uncontrolled high blood pressure or ischemic heart disease.

  Another triptan medication, zolmitriptan (Zomig), can be taken orally for relief of cluster headache. Although oral zolmitriptan isn't as effective as injectable sumatriptan, it may be an option for people who can't tolerate other forms of acute treatment. Researchers are also investigating the use of the nasal spray form of zolmitriptan for cluster headache.

• Dihydroergotamine. This ergot derivative is available in injectable and inhaler forms. Dihydroergotamine (D.H.E. 45, Migranal) is an effective pain reliever for some people with cluster headache. When administered intravenously, the drug requires you to go to a hospital or doctor's office to have an intravenous (IV) line placed. The inhaler form of the drug works more slowly. The dosage must be limited to avoid side effects, especially nausea.
• Local anesthetics. The numbing effect of local anesthetics, such as lidocaine (Xylocaine), may be effective against cluster headache pain when used in the form of nasal drops.

Surgery
Rarely, surgery is recommended for people with chronic cluster headache who don't respond well to aggressive treatment or who can't tolerate the medications or their side effects. Candidates for surgery must have headaches only on one side of the head because the surgery can be performed only once. People with headaches that alternate sides of the head risk the chance that the procedure will be unsuccessful.

Several types of surgery have been used to treat cluster headache. These procedures attempt to damage the nerve pathways thought to be responsible for pain. However, residual muscle weakness in your jaw or sensory loss in certain areas of your face and head may result. The most common procedures are directed at the trigeminal nerve.

• Conventional surgery. Using a conventional invasive procedure, the surgeon cuts part of the trigeminal nerve with a scalpel or uses small burns to destroy part of the nerve. This form of surgery provides relief for about three-fourths of people with chronic cluster headache.
• Radiosurgery. In a procedure called radiosurgery, a focused beam of radiation is used to destroy part of the trigeminal nerve. Radiosurgery is a noninvasive procedure with fewer side effects than conventional surgery, but the effectiveness, safety and permanency of the results aren't well established.

Potential treatments
As scientists learn more about the causes of cluster headache, they're able to develop more selective treatments for the condition. A recent development that shows promise is the use of a device to stimulate the occipital nerve, which influences the trigeminal nerve. To treat people with frequent cluster headaches, researchers are testing a stimulator — a pacemaker-sized device that sends impulses via electrodes — that is implanted over the occipital nerve. With the stimulator in place, the recipient's attacks may subside and he or she can remain pain free for months.

Similar research is under way using an implanted stimulator in the hypothalamus, the area of the brain associated with the timing of cluster periods. Stimulation of the hypothalamus in an individual with severe, chronic cluster headache produced complete and long-term pain relief with no significant side effects.

In addition, new medications are being studied for use in treating and preventing cluster headache.

Because the cause of cluster headache is unknown, you can't prevent a first occurrence. However, a preventive strategy is crucial for managing cluster headache because trying to treat it only with acute drugs can seem hopeless. Prevention can help reduce the frequency and severity of the attacks and the risk of rebound headaches. Preventive medications can also increase the effectiveness of acute medications.

Preventive medications for cluster headache are generally used for either a short-term (transitional) strategy or a long-term (maintenance) strategy. The short-term medications work quickly but may have undesirable side effects. Long-term medications take effect more slowly but can be used safely throughout the cluster period.

Whenever a cluster period starts, you'll likely start taking a long-term medication, many times accompanied by a short-term medication. After a couple of weeks, you'll discontinue use of the short-term medication but continue with the long-term drug.

Short-term prevention
Short-term medications can prevent headache attacks during the period of time it takes for one of the long-term drugs to become effective. The main short-term preventive medications are corticosteroids and ergotamine. A nerve block may also be effective, particularly for some people who can't tolerate the other medications.

• Corticosteroids. Inflammation-suppressing drugs called corticosteroids, such as prednisone (Deltasone, Sterapred, others) and dexamethasone (Decadron), are fast-acting preventive medications. They belong to a general family of medicines called steroids. Corticosteroids may be prescribed if your cluster headache condition has only recently started or if you have a pattern of brief cluster periods and long remissions. While corticosteroids are an excellent treatment for several days, serious side effects make them inappropriate for long-term use.

• Ergotamine. Ergotamine (Ergomar), available as a tablet that you place under your tongue or rectal suppository, can be taken before bed to prevent nighttime attacks. Ergot medications are effective for short periods but shouldn't be used for more than two to three weeks.
• Nerve block. Injecting an anesthetic (numbing agent) into the fibers around the occipital nerve, located at the back of the head, can prevent pain messages from traveling along that nerve pathway. The occipital nerve converges with the trigeminal nerve, which connects to all the pain-sensitive structures in the skull. An occipital nerve block can be useful for temporary relief until long-term preventive medications take effect.

Long-term prevention
Long-term medications are taken during the entire cluster period. Some of people with chronic cluster headache don't respond well to the use of one long-term medication. In this situation, your doctor may recommend that you take two or more long-term medications simultaneously.

• Calcium channel blockers. The calcium channel blocking agent verapamil (Calan, Covera, Isoptin) is often the first choice for preventing cluster headache, although the way verapamil works with cluster headache isn't well understood. The medication may be used from the start of a cluster period until three to four weeks after the last headache. Then its use is gradually tapered and discontinued under your doctor's direction. Occasionally longer term use is needed to manage chronic headache. Constipation is a common side effect of this medication, as well as dizziness, nausea, fatigue, swelling of the ankles and low blood pressure.

• Lithium carbonate. Lithium (Lithobid), which is used to treat bipolar disorder, is also effective in preventing chronic cluster headache. Side effects include tremor, increased thirst, diarrhea and drowsiness. Your doctor can adjust the dosage to minimize side effects. While you're taking this medication, your blood will be drawn at regular intervals to check for the development of more serious side effects, such as liver or kidney damage.

Preventive medications under evaluation
Promising preventive medications for cluster headache include the hormone melatonin, capsaicin (Zostrix) — a cream that affects nerves near the skin — and anti-seizure medications such as divalproex (Depakote), gabapentin (Neurontin) and topiramate (Topamax). Injections of botulinum toxin type A (Botox), a wrinkle-smoothing drug, may provide relief for some people with cluster headache who don't respond to conventional medication. More studies are needed to evaluate the effectiveness of all these treatments for cluster headache.

In addition, you may help reduce your risk of future attacks by avoiding alcohol and nicotine, which often precipitate cluster headaches.

The following measures may help you avoid a cluster attack:

• Stick to a regular sleep schedule. Cluster periods often begin when there are changes in your normal sleep schedule. During a cluster period, follow your usual routine.
• Avoid afternoon naps. Once a cluster period has started, taking an afternoon nap brings on a headache for many people.
• Avoid alcohol. Alcohol, including beer and wine, almost always triggers a headache during a cluster period. This can happen quickly, even before you finish the first drink.
• Limit exposure to volatile substances. Prolonged exposure to substances such as solvents, gasoline and oil-based paints may trigger an attack.
• Be cautious in high altitudes. During a cluster period, the reduced oxygen at altitudes over 5,000 feet may trigger a headache. There may be drug interactions between medications for cluster headache and medications for mountain sickness such as acetazolamide (Dazamide, Diamox, others).
• Avoid tobacco products. Nicotine may trigger a headache during a cluster period. If you're prone to cluster headache, it's best to stop smoking and avoid other tobacco products.
• Avoid glare and bright lights. For some people, excessive glare and bright lights can bring on a headache.

Living with cluster headache can be difficult. In addition to the physical symptoms, the chronic pain that often accompanies cluster headache attacks can make you anxious or depressed. Ultimately, it may affect your interaction with friends and family, your productivity at work, and the overall quality of your life.

You may find that talking to a counselor or therapist can help you cope with the effects of cluster headache. Or you may find encouragement and understanding in a headache support group. Although support groups aren't for everyone, they can be good sources of information. Group members often know about the latest treatments and tend to share their own experiences. If you're interested, your doctor may be able to recommend a group in your area.