Cluster headache

Cluster headache is a distinctive headache that is regarded by most neurologists as a variant of migraine, which affects more males than does the more common form of migraine, seen in higher numbers in women.

Definition
The International Headache Society has published strict criteria for the diagnosis of cluster headache which are as follows:

(1) Severe unilateral headache in the orbital, supraorbital, or temporal region lasting 15 minutes to 3 hours.
(2) The frequency of headache must vary between 1 every other day up to 8 per day
(3) The headache must be associated with either:
• lacrimation (eye tearing)
• nasal congestion
• rhinorrhea (runny nose)
• forehead/facial swelling
• miosis (small pupil)
• ptosis (eyelid partially closed)
• eyelid edema
• conjunctival injection (redness in the white part of the eye)
• sense of restlessness or agitation during the headache
(4) No other associated disease

Practical issues and explanations
Why the term 'cluster'?
Typically there will be a flurry of recurrent, severe, 1-sided headaches at least 1 a day if not more, often at the same time of each day or night, lasting 1 to 3 hours then remitting, only to reappear at the same time the following day. These recurrent headaches may persist for several weeks then stop as quickly as they started. Then, having not had any headaches for months or even years, another cluster suddenly begins.

The second unusual characteristic of these headaches is that they more typically begin at night when a person is asleep. The sufferer will be well during daylight hours, go to bed feeling fine, and then wake up, usually around the same time each night or early hours of the morning, with a disabling headache. Some people are so disabled by their headaches that they are terrified of going to bed.

For each individual patient the interval between the "cluster" of recurrent headaches is the same. For example, one person may have a cluster of headaches lasting a few months every year, sometimes even beginning in the same month of every year, while another may have a cluster of headaches lasting weeks or months but only every 7 years. It is quite predictable within an individual. What is it that makes this headache come on at about the same time every night during a cluster, and at the same time interval between cluster attacks? This is part of the fascination and conundrum of cluster headache, which has defied rational explanation, although there are many theories.

The pain
By definition the pain must be only on 1 side of the head. The term mentioned above, "orbital," is the medical term for the contents of the eye socket. For the vast majority of people with cluster headache the headache stays on the same side during each cluster episode, rarely it may change to the other side, but not during the same cluster of headaches. It is often felt to be at its worst in and around the eyeball on that side of the skull. The character of the pain is said to be deep, boring, and aching and so severe that it is sometimes described as feeling like someone is hammering a red hot poker into the brain through the eyeball. Whereas in typical migraine people will usually go to bed, preferring to lie still and sleep them off, in cluster headache the opposite applies; driven to distraction, the person with a cluster headache will pace their bedroom at night clutching the side of their head and sometimes applying ice to the forehead and cheek region in an effort to relieve the pain. Some people explain that they feel like banging their heads against a wall or gouging out their eyeball in the hope that it will relieve the pain.

It is now believed, after much scientific research, that the way in which we feel the pain of a headache, whether a migraine or a cluster headache, arises from the distention and sterile inflammation often closely seen around the blood vessels over the skull and in certain structures within the brain itself. The pain fibers travel in a specific nerve that supplies feeling to the face, called the trigeminal nerve. The fibers carrying the painful stimulus project back into the brainstem and also into the spinal cord, specifically the cervical cord.

Associated symptoms
• lacrimation (eye tearing)
• nasal congestion
• rhinorrhea (runny nose)
• forehead/facial swelling
• miosis (small pupil)
• ptosis (eyelid partially closed)
• eyelid edema
• conjunctival injection (redness in the white part of the eye)

To make a confident diagnosis of cluster headache at least 1 of these symptoms must be present and most sufferers will have at least 1 if not 2; rarely would a patient have all 8 symptoms.

A word now of explanation about the subconscious nervous system, which controls many of these "associated symptoms." It is called the autonomic nervous system, although a more understandable term would be "automatic." The autonomic or "automatic" nervous system works subconsciously. For example, the autonomic nervous system stimulates the heart to beat regularly, on average 72 beats per minute. It also stimulates the lungs to breathe between 12 and 15 times a minute. These events occur without us being aware. Similarly, the manifestations during a cluster headache of a watery eye, a runny nose, a swollen red face, or a small pupil are all usually controlled by the autonomic nervous system. Many of these nerve fibers reached the various tissues of the body by wrapping themselves around the blood vessels that supply the same tissues.

Cause of cluster headache
As described above, reasonable scientific evidence supports theories in relation to
• The pain and how and why people feel it
• The associated symptoms arising from involvement of the autonomic nervous system

Just behind each eyeball is an extremely complex "tangle" of blood vessels and nerves: both those that are responsible for feeling pain from the trigeminal nerve as well as those autonomic nerves that travel along together with the blood vessels. This particular complex structure of blood vessels and nerves is called the sphenopalatine ganglion. It is now widely believed that there is some intermittent acute derangement of the structures in cluster headache

The conundrum of cluster headache
The most fascinating aspect of this type of headache is why it occurs in clusters with such a stable and predictable frequency, seemingly unique for each individual sufferer. Why is it that one patient might have clusters occurring every 6 months, the next patient every year, and another every 4 years? Moreover, what is it about sleep or nighttime that seems to provoke these headaches? These are rhetorical questions to which there are not yet definitive answers. However, there is one area of the brain that seems to be responsible for monitoring and reacting to the cycle of night and day (diurnal rhythm), it is called the hypothalamus. A common example of how this particular area of the brain can be "tricked," is the phenomenon of jet lag. A lot of research is now being undertaken to see just what happens in the hypothalamus and why it may be responsible for setting off the pattern of cluster headache attacks.

Treatment
In general, the drugs used for treating acute cluster headache and long-term prevention of cluster headache are much the same as those used for migraine headache. It is important to understand that the treatment of headaches, both migraine and cluster headaches, involves 2 different treatment options.

• Abortive therapy: This is what the patient takes when they have a severe headache in an effort to relieve the pain and symptoms. The best example of this type of drug is sumatriptan, which can be administered either by mouth, or for a rapid effect, as a nasal spray. Dihydroergotamine (DHE 45) has been used to treat migraine headaches acutely for many years; it is relatively cheap and can also be administered either as an injection or a nasal spray, and despite the fact that it appears to be "old-fashioned" it has nevertheless proved to be effective in ending a cluster headache.

There is an interesting aspect of cluster headache that is quite unique, and possibly a diagnostic of the headache type: cluster headache will be quite rapidly and almost miraculously dissipate by the inhalation of oxygen, usually around 10 liters per minute for 2 or 3 minutes at most. Indeed, there are some neurologists who would say that the failure to respond to oxygen means that the headache is less likely to be a true cluster headache.

• Prophylaxis: If the headaches become very frequent, sometimes patients will be advised to take medication on a daily basis, even though they do not have a headache, in an effort to prevent or reduce the number of attacks. This is called "long-term prophylaxis." It is important to understand that treatment choices are often very different for each treatment modality. Drugs that are used to stop the headache are not used for prevention, and similarly most drugs used for prevention are not useful during a severe headache attack. It is also important to stress that preventative medication usually requires several days or even weeks to build up and exert its effect, so do not be dismayed if within a few days of starting preventative treatment the cluster headaches still occur.

• Verapamil is classified as a "calcium channel blocker" and is effective.
• Methysergide, cyproheptadine, and indomethacin have also been shown to be effective.

Whether or not long-term prevention is required depends on the individual patient.

In a small proportion of patients, however, cluster headaches can become so persistent that they occur on a daily basis, without ever showing any sign of ending. In this case they are called chronic cluster headaches. It is sometimes extremely difficult to distinguish between common migraine and this type of cluster headache. In this rather unique situation, your neurologist may recommend a short course of high-dose steroids, such as prednisolone, perhaps lasting a month or so.

Lithium appears to be particularly effective for the chronic form of cluster headaches, but when taken for any length of time there are possible side-effects including the disruption of thyroid function, which needs to be monitored by your neurologist.

This information was written by Graham Norton FRACP, and is herewith used with permission. It was last reviewed February 1, 2013.

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