A cluster bout is a period of time during which individual cluster headache attacks occur.
There are two types of cluster headache, which are classified according to the duration of the cluster bout: Episodic Cluster Headache (ECH) and Chronic Cluster Headache (CCH).
1. Episodic Cluster Headache (ECH)
Approximately eight out of ten sufferers of cluster headache have ECH, which is diagnosed when they have a series of bouts, each one lasting more than a week and separated by pain-free remission lasting more than two weeks. Most ECH sufferers have one or two cluster bouts per year, each lasting between 1-3 months. Often, these bouts tend to start during the same month[s] of the year. Although the duration of the cluster bout and the period of remission vary between individuals, these periods tend to remain relatively consistent within the same individual.
2. Chronic Cluster Headache (CCH)
The remaining 20% of CH sufferers have CCH, whereby no pain-free remission occurs within one year, or the remission periods last less than four weeks.
There is only a small amount of literature available regarding the long-term outcome of CH, but all the available evidence suggests that it is a lifelong disorder amongst the majority of sufferers.
In one study, about one in ten ECH sufferers became CCH sufferers whereas a third of CCH sufferers became ECH sufferers. A very encouraging piece of information for CH sufferers is that many of them can expect to develop longer periods of remission as they get older.