Cluster Headache – One Of The Most Painful Conditions Known To Mankind

Cluster headache is a devastating and debilitating disease that affects approximately 7 million people worldwide. It is characterized by highly intense headache attacks which are usually located around one eye and can last for up to three hours. The attacks often occur in clusters, reappearing up to eight times daily during a period of weeks to months, and are then in a majority of patients followed by a symptom-free remission period lasting for months to years. The headache is accompanied by one or more autonomic symptoms, such as tearing, reddening of the eye, runny nose or nasal congestion, as well as restlessness.

The pain has been described as the worst pain known to mankind, and cluster headache has, in addition, received the notorious nickname “suicide headache” because of reports on suicide attempts to evade the pain when treatment is insufficient. The suicide rate for cluster headache patients is 20 times the national average. A global survey asked 1,500 cluster headache patients to rate cluster headache attacks and other painful conditions that they may have experienced on a scale from 1 to 10 and it could clearly be concluded that the pain of cluster headache stands out (9.7) compared to childbirth (7.2), kidney stones (6.6), migraine (5.4), or a gunshot wound (6.3).1

Many people have never heard of cluster headache, and there is still sometimes the misconception that headache disorders are psychosomatic. However, research has shown that there is a neurovascular basis to headaches which explains the pain and accompanying symptoms. Blood vessels in the head region dilate which stimulates pain receptors on nerve endings in close proximity and send a message to the brain that there is a pain in the head and/or face region. The causes for primary headaches (i.e. not caused by other conditions, such as head trauma or infection) have yet to be determined.

For cluster headache, several hypotheses have been proposed including a disturbance in circadian rhythm (circa= about; diem= day) in the affected. Many organisms, from bacteria to humans, are equipped with an endogenous biological clock which drives these 24-hour rhythms. This clock is very important to align our sleeping and feeding behavior to the light-dark cycle of the Earth. In a majority of cluster headache patients, the attacks follow a circadian pattern, meaning that their headache attacks reoccur at specific times of the day. Additionally, about half of the patients also exhibit circannual rhythmicity where the headache clusters reappear during specific times of the year.

In a paper published recently in Cephalalgia, our group has characterized the cluster headache population in Sweden.2 The patients completed a questionnaire regarding attack patterns, triggers, use of medications, and lifestyle factors. What is more, we developed a new severity index for grading cluster headache, the Cluster Headache Severity Scale (CHSS), in order to identify patients with a very high disease burden.

68% of the 500 cluster headache patients were men which supports the observation that the disorder is more common in men than in women.3 Disease onset is reported to be between 20 and 40 years of age, and, in the Swedish cohort, the average age at onset was 31 years. One out of ten patients stated having a close relative also diagnosed with cluster headache, indicating a hereditary component.

As previously mentioned, circadian rhythmicity may play a crucial role in cluster headache, and about two-thirds of Swedish cluster headache patients reported recurring headache attacks at specific times of the day. There is a clear peak of attacks during night time between 2:00 am and 4:00 am, whereas the lowest frequency of attacks occurs between 10:00 am and 2:00 pm. In addition, we saw that cluster headache patients with high CHSS scores reported fewer hours of sleep compared to patients with lower scores.

The most common trigger factor for headache attacks when in a cluster period is alcohol, as specified by more than half of the patients. Other common trigger factors that can provoke an attack during a cluster period are stress, weather (including heat, cold, and wind), specific foods or beverages, relaxation/sleep, or, on the contrary, sleep deprivation.

The most used successful abortive medication for cluster headache are triptans, such as sumatriptan, or oxygen, which both lead to a constriction of blood vessels, thereby easing the pain within 15 minutes. But, in particular, triptans are very unspecific, not to mention inefficient in around 30% of cluster headache patients, and cause a series of side effects such as head pain and nausea.

According to several studies, cluster headache patients smoke cigarettes more frequently than the general population. About 29% in our cohort were current smokers as compared to 12% of the general Swedish population. We identified a delayed disease onset in current or previous smokers with cluster headache compared to non-smokers, which could suggest that smoking is a type of self-medication for cluster headache due to its vasoconstrictive properties and thereby delaying disease onset.

Not surprisingly, alcohol consumption was identified to be much lower in cluster headache patients with a higher disease burden (high CHSS score), since alcohol is a common trigger factor. Women with cluster headache specify more often that they do not drink alcohol at all (47%) compared to women of the general Swedish population (18%).

This study characterizes the cluster headache population in Sweden and demonstrates how profoundly affected the daily lives of this patient group is. Headache disorders are still underappreciated by many healthcare systems according to the World Health Organization, although they produce high costs for the healthcare systems.4 More research needs to be done in this field in order to support this patient group and find more effective treatments.

These findings are described in the article entitled Cluster headache – clinical pattern and a new severity scale in a Swedish cohort, recently published in the journal Cephalalgia.


  1. Schor LI. Cluster Headache: Investigating severity of pain, suicidality, personal burden, access to effective treatment, and demographics among a large International survey sample. Cephalalgia. 2017;37:172
  2. Steinberg A, Fourier C, Ran C, et al. Cluster headache – clinical pattern and a new severity scale in a Swedish cohort. Cephalalgia. 2018;38:1286–1295
  3. Headache Classification Committee of the International Headache Society (IHS). The International Classification of Headache Disorders, 3rd edition. Cephalalgia. 2018;38:1–211
  4. Polson M, Lord TC, Evangelatos TM, et al. Real-world health plan claims analysis of differences in healthcare utilization and total cost in patients suffering from cluster headaches and those without headache-related conditions. Am J Manag Care. 2017;23:S295–S299