Chronic headaches: from research to clinical practice.

Chronic daily headache (CDH) is a heterogeneous group of headaches that includes primary and secondary varieties. Primary CDH is a frequent entity that probably affects 4-5% of the population. It can be subdivided into headaches of short duration (<4 h/attack) like chronic cluster headache, and disorders of long duration (>4 h/attack). Primary CDH of long duration includes transformed migraine, chronic tension-type headache, and new daily persistent headache and hemicrania continua. Analgesics, ergots and triptan overuse are frequent in all types of CDH. We revise recent insights into the epidemiology, pathophysiology, clinical characteristics and prognosis of CDH.