Cluster Headache (CH) is one of a group of 'primary' headaches named Trigeminal Autonomic Cephalgias (TACs). There are three other types of TAC, namely Paroxysmal Hermicrania (PH) , SUNCT Syndrome [Short lasting unilateral headache with conjunctival injection and tearing], and Hemicrania Continua [HC]. Primary headaches are defined as those where the headache is the condition itself, as opposed to 'secondary' headaches, which are caused by external factors, such as accidents or infection.
These types of TAC can be identified by the fact that severe pain focuses on one side of the head (often including the face and eye), together with other symptoms occurring on the same side as the pain, called 'cranial autonomic' symptoms (CAS).
These symptoms are called 'autonomic' because they are involuntary or automatic responses, not caused by any conscious effort or external forces. They include reddening and watering of the eye, a runny or blocked nostril, droopy eyelid, constriction of the pupil, flushing and facial sweating. If none of these autonomic features occur at the same time as the headache, then they are more likely to be other types of short-lasting headache (see separate links).
The first three listed TACS have relatively short lasting pain attacks. Defining 'short lasting' headaches is difficult, but as a guideline, the period of pain for most TACs is less than four hours, compared with migraine headaches, which tend to last for more than four hours. HC attacks can last for several hours with exacerbations in the pain levels.
The key feature of these TACs is the severity of pain involved, and unlike other severe headaches, there is often a sense of restlessness or agitation during the period of pain, during which the sufferer finds it impossible to keep still.
It is extremely important to differentiate between these TACs, because the appropriate treatment for each type is very different. They are all relatively rare, when compared to migraine, for example, which is one of the reasons why GPs may fail to diagnose them. The importance of recognising and differentiating between these conditions is crucial, as they often show an excellent response to the right treatment.
