There are 2 major forms of cluster headache, namely, episodic cluster headache and chronic cluster headache (Headache Classification Committee of The International Headache Society 2004). The term “attack” generally is used to refer to a distinct attack of pain, whereas a bout is a series or “cluster” of attacks. Thus, episodic cluster headache is characterized by bouts lasting 7 days to 1 year separated by remission periods lasting 1 month or longer. Chronic cluster headache is characterized by the absence of remission for 1 year or short remissions of less than 1 month. Both classifications assume no preventive treatments. Patients’ cluster headaches may evolve from the episodic to the chronic form with sporadic, late-onset attacks, a high frequency of cluster periods, and short-lived duration of remission periods when the headache is still the episodic form, all correlating with the transition to the chronic form (Torelli and Manzoni 2002). Chronic cluster headache may be seen de novo (primary), or it may evolve from the episodic form (secondary); differences between the 2 include earlier cluster headache onset and duration of attacks varying more frequently between 120 and 180 minutes (Torelli et al 2000), although in practice this distinction seems to have no clinical utility (Donnet et al 2007). Cluster headache is extremely disabling when patients are experiencing a bout (D'Amico et al 2002). Even with chronic cluster headache, cycling can occur (Irimia et al 2008b), which could be called “micro-cycling”; a similar phenomenon is seen in SUNCT (Irimia et al 2008b).
The attack consists of the rapid onset of headache that builds to a peak in about 10 to 15 minutes and lasts for approximately 30 to 180 minutes, although longer attacks are not infrequent (van Vliet et al 2006a). The headache is almost always unilateral. In order of decreasing frequency, common sites of pain are: orbital, retro-orbital, temporal, supraorbital, and infraorbital. The head pain occasionally switches sides, and in extremely rare cases it can be bilateral. Typically, the pain is in the trigeminal nerve distribution, but extra-trigeminal pain, especially in the suboccipital area, is known to occur. Rarely, attacks may occur without cranial autonomic symptoms, although in each such case we have seen, the patients have had typical agitation and restlessness. Cranial autonomic symptoms can also occur alone (Martins et al 2005), typically in patients who have been treated with nerve root sections (Matharu and Goadsby 2002). The number of attacks per day varies, usually from 1 to 3, but the International Headache Society classification allows from 1 every second day to 8 per day. More frequent or treatment-resistant attacks should lead to consideration of other trigeminal-autonomic syndromes, such as paroxysmal hemicrania. Migrainous features, such as nausea, photophobia, and phonophobia, can be present in as many as half of cluster headache cases (Bahra et al 2000b). Moreover, between 6% (Silberstein et al 2000) and 14% (Bahra et al 2000b) of patients report typical migraine aura with their cluster headache. Hemiplegic aura has been reported (Siow et al 2002). This needs careful evaluation from a diagnostic viewpoint. Cluster headache is well-recognized in children (McNabb and Whitehouse 1999; Lampl 2002), and this author has seen a 3-year-old child with a convincing story, although it may begin as late as 89 years of age (Fischera et al 2005).
One remarkable aspect of cluster headache is its periodicity, with attacks often occurring at almost the same time every day (Ekbom 1970); this phenomenon has resulted in suggestions that human circadian pacemaker physiology is involved. Nocturnal attacks occur during both REM and non-REM sleep periods (Kudrow et al 1984). Sleep studies show reduced REM sleep in cluster headache (Barloese et al 2014a). Attacks are characterized by excruciating pain that is regarded by sufferers, without exception, as the worst pain that they have ever experienced. The pain is associated with ipsilateral cranial parasympathetic overactivity, lacrimation, conjunctival injection and nasal stuffiness or rhinorrhea, and an ipsilateral partial (third neuron) Horner syndrome (Drummond 1988) with ptosis and miosis. These symptoms are equally likely in episodic and chronic cluster headache (Gaul et al 2012). In exceptional cases, the cranial autonomic symptoms can result in obvious swelling (Attanasio et al 2000) or even nose bleeds. Although less common than in migraine, photophobia and phonophobia occur in cluster headache (Vingen et al 1998) and when present are more often lateralized to the side of the pain (Irimia et al 2008a).
Neurologic examination may reveal mild ptosis and miosis on the side of the headache, especially during or immediately following the attack, and from time to time impaired trigeminal sensation, although the latter will trigger a search for a lesion. Ipsilateral tenderness of the carotid artery, periorbital swelling, and congestion of the conjunctiva are also noted. During a bout, a subtle but convincing, mild, partial Horner syndrome ipsilateral to the pain is often present. Alcohol, nitroglycerin, and histamine can induce attacks during cluster periods (Horton et al 1939; Ekbom and Kugelberg 1968). Allodynia and interictal pain is seen in cluster headache (Lance and Goadsby 2005; Marmura et al 2010) and is almost invariably found in patients who also have a personal or family history of migraine.