Abstract
Cluster headache (CH) emerged as an entity from the much more common ‘megrim’ in the C17th. Its diagnostic features were first codified in 1962, and it has been considered a distinct, specific primary headache in all subsequent classifications. However, in recent years it has become clear that a significant proportion of CH patients have semiologies that do not conform to the defined criteria, contributing to delays in diagnosis and management. We have proposed previously that primary headaches are a semiological continuum, and consistent with this ‘migraine’ can transform to CH, and both semiologies can manifest in an individual, sequentially or concomitantly. While CH remains uniquely, the only primary headache which is more common in males, there has been a significant decline in the M:F ratio in the last decade, and women generally suffer more severe attacks than men. The temporal ‘clustering’ of headache attacks, from which the condition derives its name, is not confined to CH, and the restlessness and agitation which can occur during CH attacks, but never in migraine, does not affect all CH patients. Recent studies indicate that it may be a movement disorder rather than a ‘psychic’ response to the extreme head pain.
Cluster headache appears to have a stronger genetic contribution to its pathogenesis than migraine, but despite extensive efforts, no specific genetic signatures for these conditions have emerged. Psychometric studies have revealed differences in mood, emotion and behaviour between migraineurs and CH patients, and tobacco smoking currently remains the strongest risk factor for CH. Thus, while the archetypical CH identity remains distinct there are substantial overlaps with migraine, and at present the only categorical semiological difference between them is the significantly shorter headache duration in CH.