What Is Cluster Headache?

Have you ever had a burning or piercing headache on a daily (or near daily) basis that lasted for weeks or months? Was this near your eye or on one side of your head?¹ What you experienced may have been a cluster headache. In this article, we’ll outline what cluster headache is, its causes and risk factors, how it’s diagnosed, and the available treatment options. 

Definition of cluster headaches 

Cluster headaches are a severe type of headache that typically occur in periods of frequent attacks known as clusters. A single attack can last between 15 minutes and three hours and happen multiple times a day. Each cluster  can last from two weeks to three months. The International Classification of Headache Disorders (ICHD) classifies two types of cluster headaches:

• Episodic - Episodes last between 7 days to a year and include at least three months of no pain symptoms (remission). 
• Chronic - Episodes last for a year or longer and include less than three months of no pain symptoms or no remission period at all.

Cluster headaches are not linked to an underlying condition and fortunately are quite rare.

Symptoms of cluster headaches 

The onset of a cluster headache is fairly quick and comes with no warning. Occasionally, it can start with migraine-type sensations such as aura (temporary visual or other disturbances) and nausea. Other symptoms can include:

• Stabbing or sharp pain, commonly around the eye area, that can spread to the face, neck, and head
• Pain on one side of the head that can alternate sides with each cluster
• Feeling restless
• Eye redness on the affected side
• Runny or congested nose on the affected side
• Sweating of the forehead or face
• A change in skin colour on the affected side
• Eye swelling on the affected side
• Eyelid drooping on the affected side³

Causes of cluster headaches 

What causes cluster headaches is unknown. However, they are believed to occur due to hyperactivity in the hypothalamus of the brain.⁴ The hypothalamus is a region of the brain that is involved in controlling the body’s circadian rhythm (i.e. the internal body clock that enables physical, mental, and behavioural changes to follow a 24-hour cycle). This could explain the regularity in timings of cluster headache episodes.⁴

Chemicals called neurotransmitters are released by the hypothalamus, which in turn stimulate brain nerve cells causing pain and associated symptoms. This can also result in vasodilation (opening up) in the blood vessels. This can happen at the specific side of the head where symptoms are experienced.⁴

It is important to note that the above are simply theories and the exact cause of cluster headaches is not known.⁴

Triggers for cluster headaches

The majority of cluster headache episodes happen for no identifiable reason. The likelihood of experiencing a cluster headache may be hereditary (genetic link).⁴

If someone affected by cluster headaches identifies a trigger for them, they are advised to avoid this trigger, especially during an episode.⁴

Below are a few examples of potential triggers: 

Smoking

Cluster headaches are statistically more common in smokers than non-smokers.⁴ Smokers are also known to experience more extreme symptoms. 

Alcohol

Often, people affected by cluster headaches experience the onset of a pain attack about an hour after drinking alcohol. For this reason, it is recommended to avoid alcohol during episodes. 

Heat

A higher-than-usual body temperature may trigger a cluster headache episode. This can include and is not limited to, having a hot bath or exercising in a hot room.

Strong scents

Strong scents such as petrol, perfumes, and solvents may induce a cluster headache episode.⁴

Tumour

Most people affected by cluster headaches do not show any difference in brain scans compared to non-sufferers. However, a very rare percentage of sufferers have a pituitary adenoma (tumour in the pituitary gland, which is located at the base of the brain) or other types of brain tumours.⁴

Risk factors for cluster headaches

Some of the risk factors of a cluster headache are: 

Sex

Cluster headaches are more common in people assigned male at birth (AMAB) than people assigned female at birth (AFAB).

Age

Although cluster headaches can happen at any age, the age of onset is  most common between  20 and 50 years old.

Smoking

Most people affected by cluster headaches are smokers. However quitting smoking does not necessarily relieve symptoms.

Alcohol

People affected by cluster headaches experience a higher incidence of future episodes when they drink during an episode.

Family history

Being related to someone who suffers from cluster headaches may increase your chances of experiencing them.³

Diagnosing cluster headaches

A neurologist (a specialist doctor trained in disorders of the brain and nervous system) can assess and diagnose cluster headaches.³

Typically, a diagnosis of cluster headache is dependent on medical history and the following information about the pain experienced:

• Severity of the pain
• Location of the pain
• How often headaches are experienced
• How long each episode lasts
• Other association symptoms³

A physical and neurological exam may also be conducted which involves testing your reflexes, senses, and nerves. 

In some cases, if the neurological examination is not enough, the doctor will recommend further tests including a brain scan, to rule out other possible causes of the pain. Magnetic resonance imaging (MRI) and computerised tomography (CT) scanning are the most commonly used imaging techniques:

Magnetic Resonance Imaging (MRI) scan

An MRI uses radio waves, coupled with a strong magnetic field, to produce a comprehensive image of the brain. MRI scans can assist in diagnosing an array of brain and nervous system conditions including strokes, infections, tumours, and bleeding.³

Computerised Tomography (CT) scan

In a CT scan, detailed cross-sectional images of bones and soft tissues are produced using a series of x-rays. These can detect brain damage, infections, bleeding, and tumours as well as other causes of headaches.³

Treatment of cluster headaches

Traditional oral painkillers (such as paracetamol and ibuprofen) are not always suitable for cluster headaches, as the episodes are usually over by the time the painkillers take effect.⁴

Treatment options for cluster headaches fall into  two categories: treatments to relieve/stop pain (known as acute treatment) and treatments to prevent episodes.⁴

Treatments to relieve/stop episodes

Sumatriptan 

Sumatriptan belongs to a class (group) of drugs called triptans. Triptans are commonly used to treat migraines. They are not painkillers and target a brain chemical called 5-HT (also known as serotonin). 5-HT is thought to be responsible for cluster headaches and migraines.⁴

Sumatriptan is administered under the skin, via an injection. It is administered immediately on the onset of a headache and, in most people, provides pain relief within 15 minutes.⁴

Side effects are mild and short-lived and include tiredness, feeling nauseous, dizziness, and dry mouth.⁴

Sumatriptan is not recommended in people with stroke, heart disease, or peripheral arterial disease.⁴

Zolmitriptan 

Another triptan drug, zomitriptan, is administered as a nasal spray and often used as an alternative to sumatriptan. Zolmitriptan is effective, however, it works slower than injectable sumatriptan.⁴

Oxygen therapy 

Oxygen is delivered in a 100% oxygen cylinder via a face mask. It is used in suffers in which triptan therapy has not worked.⁴

Oxygen therapy is not recommended in patients with chronic obstructive pulmonary disease (COPD).⁴

Other treatment options 

The above are first-line treatments and have a high success rate. However, in those patients for whom they do not work, sumatriptan nasal spray and ergotamine injection may be used.⁴

Treatments to prevent episodes

There are treatment options available to prevent episodes of cluster headaches, however, research in this area is limited.⁴

Examples of treatments are:

Verapamil

Commonly used for heart conditions, verapamil may be effective in preventing episodes of cluster headaches. How it does this is unknown. The dose of verapamil used for the prevention of cluster headaches is higher than the dose used for heart conditions, so patients require regular ECG (electrocardiogram) monitoring.⁴

Lithium

Commonly known as an effective treatment option for bipolar disorder, lithium is useful in preventing cluster headaches, in particular the chronic type. How it achieves this is not fully understood, and patients require routine blood tests to monitor lithium blood levels.⁴

Methysergide

This is effective in preventing short-term episodes of cluster headaches. However, treatment must be restricted to six months due to severe side effects.⁴

Corticosteroids

People affected by cluster headaches experience positive results when using corticosteroids to prevent chronic cluster headaches. It is commonly used starting with a high dose and then a reducing regimen to break up episodes.⁴

Surgery

In extreme circumstances, where treatment options have been exhausted, patients may be offered surgery, however, long-term data on its benefits is limited. Surgery aims to disrupt the nerve paths responsible for the pain. Surgical complications may occur and include loss of sensation in parts of the face/head and weak muscles in the jaw area.³

Seek urgent medical help if:

You experience an extremely painful headache, alongside any of the following symptoms:

• Sore or painful scalp.
• Feel weak or numb in the arms or legs.
• Painful jaws, especially when eating.
• Visual disturbances such as double or blurred vision.
• Drooping eyelid/s.
• Eye pupil is smaller in one eye compared to the other ¹.

Lifestyle recommendations

Sleeping pattern can affect cluster headaches so it is important to have a consistent bedtime and hours of sleep.³

Avoiding alcohol completely can be very useful in reducing the incidence of cluster headache episodes.³

Summary

Cluster headaches are a severe type of headache that typically occur in periods of frequent attacks known as clusters. Although fortunately relatively rare, cluster headaches  can be a debilitating condition that  hugely impact a person's quality of life. Typical symptoms include sharp or stabbing pain (often around the eye area), pain on one side of the head, and feeling restless. 

The exact cause of cluster headaches remains unknown, although hyperactivity in a region of the brain called the hypothalamus is believed to play a role. 

Treatment options for cluster headaches fall into one of two categories: treatments to relieve/stop pain (such as injectable sumatriptan and zolmitriptan nasal spray) and treatments to prevent episodes (including verapamil and lithium).

Optimised treatment and daily adjustments can go a long way in managing the condition. In addition, regular sessions with a counsellor or therapist can be hugely beneficial. A local headache support group can also be useful in understanding your condition better. GPs and health care specialists can signpost you to these local services.³