Cluster headaches are primary headaches consisting of a severe stabbing pain that usually lasts between fifteen minutes and two hours and affect one side of the head, usually around the eye.
Cluster headaches can occur several times per day and characteristically come in clusters of attacks, which can last weeks or months. Individual clusters can be separated by periods of remission lasting months or years. Age of onset is usually between 20-40 years. Less than 0.5% of the population are affected and it is 3-4 times more common in men.
The causes of cluster headache are unclear but biochemical, hormonal, and vascular changes are known to induce individual attacks. Attacks seem to be linked to changes in day length, and may also be triggered (during clusters only) by alcohol, tobacco, histamine, stress or exposure to nitroglycerine. Decreased blood oxygen levels can also act as a trigger, particularly during sleep.
About 10 – 20% of patients with Cluster Headache have Chronic Cluster Headache, which is defined as attacks occurring for more than one year without remission, or with remissions lasting for less than 1 month.
I.H.S. Criteria for diagnosing Cluster Headache:
A. At least five attacks fulfilling criteria B-D
B. Severe or very severe unilateral orbital, supraorbital and/or temporal pain lasting 15 to 180 minutes if untreated.
C. Headache is accompanied by at least one of the following:
- Ipsilateral conjunctival injection and/ or lacrimation
- Ipsilateral nasal congestion and / or rhinorrhoea
- Ipsilateral eyelid oedema
- Ipsilateral forehead an facial sweating
- Ipsilateral miosis and/ or ptosis
- A sense of restlessness or agitation
D. Attacks have a frequency of one every other day to eight per day
E. Not attributed to another disorder.