A cluster headache is a severe form of headache. It causes debilitating pain that can interfere with a person’s daily life and sleep cycle.

The sharp, penetrating or burning pain associated with a cluster headache usually involves only one side of the head. This pain is most often felt in or around an eye or in the temple. Many times the head pain is accompanied by drooping of the eyelid and nasal congestion on the same side as the pain. 

One of the most painful types of headache, cluster headaches often develop within minutes. Although they offer little warning before they develop, they often occur in cyclical patterns (clusters).  They usually occur at the same time every day. In some people they occur consistently at multiple times every day. These episodes may continue for weeks or months in phases known as cluster periods.

Each individual headache episode may last an average of 45 to 90 minutes. The time between headaches within the same cluster period may last anywhere from a few hours to an entire day. Cluster periods are often followed by periods without headache. This remission period may last for months or years.

Cluster headaches that occur daily for one week to one year, followed by a remission period lasting weeks to years before the development of another cluster period, are known as episodic. Cluster headaches occurring daily for more than a year, with no remission or with pain-free phases lasting less than two weeks, may be described as chronic.

Although the exact cause of cluster headaches remains unknown, researchers have identified a number of factors believed to trigger the headaches including smoking and use of alcohol. Age and sex also appear to play a role. The majority of patients with this condition are men between the ages of 20 and 50.

To diagnose this condition, physicians will review a patient’s medical history and perform a physical examination. Imaging tests such as MRI or CAT scan may be ordered to rule out other potential causes of the head pain.

Cluster headaches cannot be cured. However, a number of treatment methods are used to relieve symptoms, shorten the headache period and prevent future episodes. Treatments include headache medications and, in some cases, surgery.

A cluster headache is one of the most painful types of headache. This uncommon condition often produces severe pain that occurs within minutes.

Cluster headaches are characterized by a sharp, penetrating, or burning pain affecting one side of the head. The pain often appears suddenly with little warning and often occurs in and around one eye or in the temple. The excruciating pain related to a cluster headache is often compared to the sensation of a hot poker being stuck in the eye. Others compare it to the feeling of the eye being pushed out of its socket. The condition may also produce a number of other symptoms including tearing of the eyes and nasal congestion.

According to the National Headache Foundation, cluster headaches affect less than 1 percent of people in the United States. About 85 percent of people affected by the condition are men, according to the American Council for Headache Education.

Cluster headaches differ from other types of headache because they occur in cyclical patterns (clusters). This type of headache occurs repeatedly every day at the same time, usually several times a day. One to four headaches a day is average. These frequent attacks may continue in a series of weeks or months (cluster periods), with each individual attack lasting an average of 45 to 90 minutes. Typically cluster periods last from two to 12 weeks. However, they can continue for more than a year. The temporary relief between attacks in a cluster period may last for a number of hours or continue for as long as a day.

The pain associated with a cluster headache often ends as abruptly as it begins, with a quick reduction in intensity. After the episode, patients are often pain-free but exhausted. The headache often goes into remission (period without headache) for some time until the pain returns. The remission period may last for months or possibly years.

Cluster headaches commonly occur at night. The abrupt onset of a cluster headache often occurs during the REM (rapid eye movement) or dreaming phase of sleep, or 90 minutes to three hours after a person falls asleep. 

Although frequency varies, most patients experience one or two cluster periods a year. In most cases, the cluster periods last between two and 12 weeks. In some people, however, cluster headaches occur for a year or more without going into remission.

The starting date and length of each cluster period is often very consistent. Many patients report that their cluster periods occur seasonally. It is also common for clusters to begin after the summer and winter solstices (the longest and shortest days of the year). Although cluster headaches occur in patterns for many people, over time they often become more frequent, less predictable and longer lasting. 

Pain usually develops on the same side of a person’s head for the duration of a cluster period. Many times, the headaches remain on the same side for a person’s entire life. Although it occurs rarely, pain may switch from one side of the head to another in subsequent cluster periods. It is extremely uncommon for pain to switch sides from headache to headache within the same cluster period.

People with cluster headaches may also have trigeminal neuralgia, a type of facial pain involving the trigeminal nerve. The combination of the two conditions is known as cluster-tic syndrome.

Cluster headaches do not pose a serious risk to a person’s overall health. However, it is a chronic condition that can cause debilitating pain. As a result, the condition can interfere with a person’s daily life and sleep cycle. In some cases, the severity of the pain becomes so unbearable that it causes people to attempt suicide.

Patients should discuss all serious or recurring headaches with their physician and seek medical attention when a headache:

• Starts suddenly
• Is severe or persistent
• Does not improve with treatment
• Disturbs sleep
• Occurs with activity
• Changes in pattern or intensity
• Is accompanied by other symptoms, such as drowsiness, vision changes, changes in movement or sensation, changes in alertness, nausea and vomiting

In some cases head pain may indicate a more serious underlying condition such as a brain tumor, stroke or aneurysm (a bulge in a weakened blood vessel with the potential to burst). As a result, patients should seek emergency medical treatment when:

• A headache is accompanied by unusual symptoms not experienced with previous headaches, including:
• • Speech problems
  • Vision abnormalities  (e.g., double vision)
  • Numbness or weakness
  • Fever
  • Stiff neck
  • Rash
  • Seizures
  • Mental confusion
    
    
• A headache occurs after a head injury
  
  
• A chronic headache intensifies with coughing, exertion, straining or sudden movement
  
  
• A new type of headache pain occurs (in those over age 50 or younger than 8)

According to the International Classification of Headache Disorders, there are two groups of cluster headaches, based on the lengths of the cluster periods and remission periods:

• Episodic. This term may be used to describe cluster headaches occurring daily in periods of one week to one year, followed by remission lasting at least one month before the development of another cluster period.
  
  
• Chronic. This term may be used to describe cluster headaches occurring daily for more than a year, with no remission or with pain-free phases lasting less than one month.
  
  

According to the National Headache Foundation, about 10 to 20 percent of people who experience cluster headaches have the chronic form. Although chronic cluster headache may develop after a phase of episodic attacks, it may also develop in people without a history of headaches. Rarely, patients may also experience alternating phases of chronic and episodic headache.

The exact cause of cluster headaches has not been identified. However, researchers believe the condition may result from several factors, including:

• Greater sensitivity of nerve pathways. The trigeminal nerve (the main nerve of the face responsible for pain and other sensations) serves the areas behind and around the eyes.
  
  
  
  
  Stimulation of the trigeminal nerve can trigger the arteries that supply blood to the head to dilate, causing eye pain. Stimulation of the trigeminal nerve also triggers activation of the autonomic nerves (which regulate involuntary bodily functions), resulting in teary eyes, drooping eyelids and congestion. Some experts believe that inflammation or abnormal activity of blood vessels in this area may also contribute to the development of cluster headaches.
  
  
• Abnormal functioning of the hypothalamus. The hypothalamus is an area of the brain responsible for controlling internal rhythms, such as hunger, thirst and the sleep-wake cycle. Many researchers believe abnormalities of the hypothalamus may explain the cyclical pattern and regularity associated with cluster headaches. A number of studies have shown an increased level of activity in the hypothalamus during a cluster headache. Studies have also discovered that people who suffer from cluster headaches have larger hypothalamuses than people who do not experience the headache. The presence of abnormal levels of certain hormones (e.g., testosterone, melatonin) during cluster periods has also been attributed to abnormalities in the hypothalamus.
  
  

• Histamine. Researchers have determined that the level of histamine in a person’s blood and urine increases during a cluster headache. As a result, many experts believe that histamines, which trigger the blood vessels to dilate, are related to the development of cluster headaches.

A number of factors may trigger a cluster headache, including:

• Smoking
• Use of alcohol
• Glare
• Changes in sleep patterns or inadequate sleep
• Certain medications that cause blood vessels to swell or widen (vasodilators), such as nitroglycerin, other nitrates and many antihypertensives (drugs for high blood pressure)

In addition, a number of factors appear to make a person more likely to develop cluster headaches. The two biggest risk factors linked to cluster headaches are age and sex. According to the American Council for Headache Education (ACHE), about 85 percent of people affected by the condition are men.

The main symptom of a cluster headache is a steady, sharp burning pain affecting one side of the head. The pain often involves one side of the face (from the neck to the temples) and frequently occurs in or around an eye or in the temple. The neck pain and facial pain may radiate to the forehead, nose, cheek or upper gum on the affected side.

Cluster headaches typically develop suddenly, often two to three hours after the patient falls asleep. The pain rapidly intensifies, typically peaking within five to 10 minutes after appearing. Peak pain may last anywhere from 30 minutes to two hours.

Cluster headaches may be accompanied by a number of other symptoms, including:

• Swelling below or around the eyes and eye pain, typically the eye on the affected side of the head
  
  
• Extreme tearing from the eye on the affected side of the head
  
  
• Redness of the eye on the affected side of the head
  
  
• Decreased pupil size
  
  
• Drooping eyelid
  
  
• Restlessness
  
  
• Red, flushed face
  
  
• Excessive sweating
  
  
• Runny nose or nasal congestion, typically affecting the nostril on the affected side of the head

In most cases, the signs and symptoms that accompany cluster headaches vanish once the head pain disappears. Decreased pupil size and drooping eyelid (Horner’s syndrome), however, can persist. In addition, a number of symptoms associated with migraines (e.g., nausea, sensitivity to light and sound, aura) can also occur with cluster headaches.

Cluster headaches can be distinguished from other types of headache because they produce a distinctive type of pain and occur in a unique pattern. As the name suggests, they come in “clusters,” with severe pain followed by remission periods. Physicians can use these symptoms to help diagnose cluster headaches.

During an evaluation for cluster headaches, physicians typically take the patient’s medical history and perform a physical examination. Information provided during these steps can help physicians determine whether a patient’s symptoms are the result of a cluster headache or an underlying medical condition (e.g., brain tumor, aneurysm).

While collecting a patient’s medical history, physicians may ask the patient to describe symptoms. Questions in a pain assessment may focus on the characteristics of the pain, including its severity, location, frequency and duration. The patient will also be asked to describe any symptoms that accompany the pain. During the physical exam, physicians may detect one-sided eyelid drooping or reduced pupil size as part of a neurological exam.  

There is no particular test to diagnose cluster headaches, so medical history and physical examination are the only way to diagnose this condition.  Other tests may be performed to rule out other serious causes of head pain.  Physicians may use a number of methods to determine the cause of the chronic or recurrent head pain. These include:  

• MRI (magnetic resonance imaging). MRIs use a powerful magnetic field to create images of structures and organs within the body, allowing a computer to produce clear cross-sectional or three-dimensional images. This test may be ordered to examine the brain and rule out aneurysm and a number of other serious causes.
  
  
• CAT scan (computed axial tomography). This test allows for multiple x-rays to be taken from different angles around the patient. A computer analyzes the “slices” or cross-sectional images. Frequently after the first set of images is taken, the patient receives an intravenous (I.V.) injection of a contrast medium (dye) to better outline the body parts. Then a second set of images is taken. This test may be ordered to examine the brain and rule out aneurysm and a number of other serious causes of pain. 

If trigeminal neuralgia or another cranial neuralgia is also suspected, the patient may undergo a neurological exam and testing such as electromyography (EMG) and nerve conduction velocity (NCV) studies.

There are a number of treatment options available for cluster headaches. Although cluster headaches cannot be cured, treatments aim to relieve symptoms, shorten the headache period and prevent future episodes.

Although they do not cure cluster headaches, prescription and over-the-counter medications may also be used to prevent headaches, stop the progression of headaches and relieve symptoms.

Pure oxygen may be recommended as a treatment method for cluster headaches, particularly those that occur at night. Administered through a breathing mask, supplemental oxygen can provide pain relief within 15 minutes. However, this type of treatment may be inconvenient, because patients must carry an oxygen cylinder and regulator with them.

A combination of headache medications may be used to treat cluster headaches and to prevent future headaches. Treating an existing headache is called acute or abortive therapy.  These medications include antimigraine medications, which include:

• Triptans, which are a type of serotonin agonist. They may be injected or taken orally or nasally. These medications may not be prescribed for patients with certain conditions, including high blood pressure, angina and some liver conditions.
  
  
• Ergotamine or ergotamine derivatives. Drugs that constrict dilated blood vessels, which often occur with headaches. This medication may be used to prevent headaches as well, but side effects can be severe (e.g., nausea, confusion, vision changes) and is often not used for more than two or three weeks. These drugs may be used with others, such as isometheptene, which reduces throbbing pain.

Other forms of medication used for acute pain relief include local anesthetics. Acute medications should be taken as soon as the attack begins. They are effective in treating the rapidly peaking pain associated with cluster headaches because they are fast-acting.

Over-the-counter drugs such as aspirin and ibuprofen are not effective in treating cluster headaches because they take too long to take effect. In most cases, the headache has disappeared by the time these medications begin to work.

There are also a number of medications used to reduce the frequency and severity of cluster headaches and increase the effectiveness of acute medications. These preventive drugs are used in short-term and long-term management strategies. Short-term drugs are fast-acting but can cause serious or undesirable side effects. The long-term medications take longer to work but can be used safely for a longer period. These medications are often taken together at the beginning of a cluster period. Patients typically discontinue the short-term medication after a couple of weeks but continue taking the long-term drug.

Short-term medications include:

• Corticosteroids. Commonly used to relieve inflammation, these drugs may be prescribed to treat cluster headaches that have recently developed. They may also be recommended for patients with brief cluster periods and long remissions. Because of the side effects and risks associated with long-term use, such as osteoporosis and diabetes, these drugs are usually taken for only a few days.
  
  
• Nerve block. An anesthetic may be injected into the fibers surrounding the occipital nerve (a nerve located at the back of the head) to prevent pain messages from traveling to the trigeminal nerve and the pain-sensitive structures in the head.  

Long-term medications include:

• Calcium channel blockers. These antihypertensives increase the flow of oxygen-rich blood to the heart, lower blood pressure and reduce the workload of the heart. They may be used from the development of a cluster period until three to four weeks following the last headache. In some cases the medication may be used for a longer period of time to treat chronic cluster headache.
  
  
• Lithium. A drug that acts on the central nervous system and is commonly used to treat bipolar disorder (manic-depressive illness), lithium is also prescribed to prevent chronic cluster headache.

Additional preventive medications include:

• Beta blockers. These antihypertensives decrease the workload of the heart and lower blood pressure.
  
  
• Tricyclic antidepressants. These drugs are commonly used to treat depression but also can help relieve some pain conditions. Antidepressants may increase the risk of suicidal thinking and behavior in children and adolescents. As a result, people being treated with these drugs should be closely monitored for unusual changes in behavior, according to the U.S. Food and Drug Administration (FDA).
  
  
• Antihistamines. These drugs are commonly used to treat allergic reactions and prevent an increase in release of histamines. However, these drugs are not usually effective in treating a cluster headache once an attack begins.
  
  
• Indomethacin. This nonsteroidal anti-Inflammatory drug (NSAID) is commonly prescribed to relieve pain, tenderness, inflammation and stiffness.

Medications used to treat cluster headaches have variable effectiveness in different people. In many cases, a number of medications may be tried before an effective drug, or combination of drugs, is found.

Though men are far more likely than women to have cluster headaches, they may be undertreated. A recently completed nine-year British study involving more than 400,000 patients found that women are more likely to seek medical help for headaches and to receive prescriptions. Anyone suffering from cluster headaches or other headaches is advised to take the initiative in seeking help. 

In addition to taking medications, patients may reduce the frequency of cluster headaches by avoiding factors that trigger the headaches. Patients may identify these triggers by keeping a headache diary for two months or longer. To compile this journal, patients record certain information after each headache occurs, including:

• When the headache occurred
• How severe the headache was
• Where the headache was located
• How long the headache lasts
• Medications taken prior to and after the headache
• Events before the headache (e.g., consumption of alcohol)
• Sleep patterns and amount of sleep

In general, there are a number of steps a patient can take to avoid a cluster headache, including:

• Avoiding alcohol because it often triggers attacks during a cluster period
• Avoiding cigarettes and other tobacco products
• Maintaining a regular sleep schedule
• Avoiding afternoon naps
• Avoiding certain medications if possible (e.g., nitroglycerin)
• Avoiding glare and bright lights

In rare instances, surgery may be recommended for treatment of chronic cluster headaches. Patients who do not respond to medication and those who cannot tolerate the side effects of medication may benefit from this form of treatment. However, surgery might be an option only for patients who experience pain on one side of their head. Because the surgery can be performed only once, patients experiencing pain on alternating sides of the head risk that the procedure will be ineffective.

A number of surgeries may be used to treat the trigeminal neuralgia that may be associated with cluster headaches (cluster-tic syndrome):

• Conventional surgery (trigeminal nerve section).  A surgeon uses a scalpel to sever part of the trigeminal nerve (the nerve in the head believed to be responsible for pain), or uses tiny burns to destroy a section of the nerve. Conventional surgery provides relief for the majority of people who undergo the procedure.
  
  
• Radiosurgery. A surgeon uses a focused beam of radiation to destroy a section of the trigeminal nerve. Although this form a surgery is noninvasive and linked with fewer side effects, the safety and permanency of the procedure have not been established. 

A number of studies on cluster headache are being conducted. Medications being studied include:

• Triptans, including nasal sprays
  
  
• Melatonin, a hormone
  
  
• Capsaicin, a cream used to deplete the neurotransmitters that help emit pain
  
  
• Anti-seizure medications
  
  
• Botulinum toxin type A, a drug used primarily to reduce the appearance of wrinkles
  
  
• LSD (d-lysergic acid diethylamide) and psilocybin, an ingredient in hallucinogenic mushrooms
  

An occipital nerve block may abort an acute attack, but research is still exploring the mechanism of this.

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about cluster headache:

1. How can I distinguish cluster headaches from other types of headaches?
   
   
2. What may be causing my cluster headaches?
   
   
3. How can I determine the cause of my cluster headaches?
   
   
4. What symptoms should I watch for?
   
   
5. What diagnostic tests might I need to undergo, and what do they involve?
   
   
6. What do my test results show?
   
   
7. Do I also have trigeminal neuralgia (cluster-tic syndrome) or another cranial neuralgia?
   
   
8. How can I expect my cluster periods and remission periods to last?
   
   
9. Are my cluster headaches likely to worsen, stay the same or improve over time?
   
   
10. How can I relieve my cluster headaches?
    
    
11. What is the best over-the-counter drug for me?
    
    
12. If medications do not help, could surgery be an option for my severe cluster headaches?
    
    
13. At what point should I call you or seek emergency treatment for a cluster headache?
    
    
14. How can I prevent cluster headaches?