Cluster headache attacks occurring for more than one year without remission, or with remission periods lasting less than one month.
A. Attacks fulfilling criteria for 3.1 Cluster headache, and criterion B below
B. Occurring without a remission period, or with remissions lasting <1 month, for at least 1 year.
3.1.2 Chronic cluster headache may arise de novo (previously referred to as primary chronic cluster headache), or evolve from 3.1.1 Episodic cluster headache (previously secondary chronic cluster headache). In some patients change occurs from 3.1.2 Chronic cluster headache to 3.1.1 Episodic cluster headache.