Histamine cephalalgia: A distinctive syndrome of headaches, also known as cluster headache or migrainous neuralgia. The common pattern of cluster headache is termed "episodic" and is characterized by 1-3 short attacks of pain each day around the eyes, clustered over a stretch of 1-2 months, followed by a pain- free breathing period (average: a year). The other main pattern of cluster headache is termed "chronic" (and is also known as chronic migrainous neuralgia). It may come out of the blue or emerge several years after an episodic pattern. It is characterized by the absence of sustained periods of remission. The episodic and acute forms of cluster headache may transform into the other, so it is clear that they are merely different-appearing patterns of one and the same disease. On the other hand, cluster headache looks different and distinct from migraine-for example, propranolol is effective for migraine but not cluster headache while lithium benefits cluster headache syndrome but not migraine-although the mechanisms underlying cluster headache and migraine may have a degree of commonality.