Cluster headache is a rare headache disorder, that manifests with strictly unilateral, very severe pain attacks that are most pronounced around the temple and eye. It is called cluster headache because it typically occurs in clusters of several weeks or months that may periodically recur, often with a seasonal preference in spring or autumn. Between these clusters, patients experience pain-free periods that often last for months or years.
The severe, unilateral pain attacks of cluster headache mostly last for 15 to 180 minutes. They often occur spontaneously, without apparent triggers. However, they tend to occur around the same time of the day every day, often waking patients from sleep. Cluster headache attacks can be triggered by alcohol, drugs (especially drugs derived from glyceryl trinitrate) and exposure to high altitudes. During an episode of cluster headache, attacks occur with a varying frequency of between once every second day and eight per day. Pain is usually side-locked in cluster headache.
Cluster headache pain is described as excruciating, gnawing, drilling, sometimes also burning. The main area of pain is usually located around or behind the eye. Some patients have the feeling that the pain radiates from their neck. Pain may also radiate towards the upper jaw.
In addition to the typical circadian periodicity, there are several accompanying symptoms that are limited to the side of the pain and are typical of cluster headache:
- Reddening of the eye
- Tearing of the eye
- Drooping of the eyelid
- Running or stuffy nose
- Sweating of the forehead or entire side of the face
- Restlessness or agitation
For diagnosis, at least one of these symptoms must be present on the side affected by the pain. Moreover, patients may suffer from symptoms as found in migraine, such as nausea, increased sensitivity to light and sounds.
These accompanying symptoms are typical of the group of so-called trigeminoautonomic headache disorders that constitute a group within the International Headache Classification. Apart from cluster headache, this group includes very rare headache disorders such as paroxysmal hemicrania and SUNCT syndrome. These headache disorders are characterized by shorter but more frequent pain attacks. They do not respond to treatments known to be effective in cluster headache.
Sometimes, cluster-like headaches occur in diseases of the ocular region or in sinusitis. Very rarely, tumours, e.g. of the pituitary gland may be at the base of cluster-like headaches. To rule out a symptomatic headache, brain imaging (magnetic resonance imaging or computed tomography) is usually performed once during the course of the disease. If both neurological examination and imaging results are normal, no additional examinations are required.
What is the cause of cluster headache?
The mechanisms underlying cluster headache are currently not known. There is some evidence that a particular brain structure, the hypothalamus, plays an important role in cluster headache. The hypothalamus is thought to constitute our “body clock” and is held responsible for the circadian rhythm and the seasonal clustering of attacks. In addition, during the attack there is activation of the pain-related structures of the trigeminal nerve and of the autonomic nervous system. The trigeminal nerve is responsible for perception of touch and pain in the face and head.
What is the natural course of cluster headache?
In most patients, cluster headache is episodic with cluster attacks occurring for periods of weeks or months, separated by pain-free periods of months or years. Rarely, cluster headache takes a chronic course, with cluster episodes lasting longer than a year or separated by pain-free periods shorter than a month. About 10% of patients suffer from a chronic cluster headache from the beginning, and about 5% of patients develop a chronic cluster headache from the episodic form.
Cluster headache – how is it treated?
Cluster headache is a primary headache disorder, and there is presently no permanent cure for this disease. However, pain intensity and attack frequency can be effectively reduced by pharmacological treatment in most cases. As in other types of headache, treatment of the acute attack is differentiated from preventive treatment.
A cluster headache attack does usually not respond to normal, over-the-counter painkillers. Many patients can stop an acute attack by inhalation of pure oxygen. This treatment is free of side effects and can be prescribed for use at home. In addition, rapidly acting triptans or nasal application of lidocaine can be used in the treatment of the acute attack.
Usually, preventive treatment is the mainstay of cluster headache therapy, as it is the only way to reduce the frequency of the extremely severe attacks. Drugs from different classes can be used. The way in which these drugs act to reduce cluster headache attacks is not known. Because cluster headache is a rare disorder, preventive treatment should be performed by a neurologist with experience in the treatment of cluster headache. Selection of the preventive drugs depends on the clinical course and on possible concomitant diseases. Frequently used drugs include verapamil, topiramate, methysergide and lithium. The effect usually sets in at 1-2 weeks. To bridge this time gap, glucocorticoids are often used. Drugs may also be used in combination. Preventive treatment is maintained until the end of the cluster episode and then tapered. As an alternative to oral drugs, repeated occipital nerve blocks (the nerve responsible for the sensation of touch and pain at the back of the head) can be performed, using local injections of local anaesthetics and glucocorticoids on the side of the pain.
Only if pharmacotherapy is not effective, operative therapies may be considered in selected patients with a severe, chronic course of the disease. Currently, there is no established operative method that allows cluster attacks to be stopped reliably and with long-lasting success in every patient. Electric stimulation of the greater occipital nerve is a promising therapeutic strategy that is currently under scientific evaluation. Before initiating an operative treatment of cluster headache, the pros and cons must be carefully considered by both the doctor and the patient and a cluster headache specialist should be involved.