Chronic daily headache.

Primary chronic daily headache can be subclassified into disorders of short duration (<4 h/attack) including chronic cluster and disorders of long duration (> or =4 h/attack). Primary chronic daily headache disorders of long duration include chronic tension-type headache, chronic daily migraine (previously called transformed migraine), new daily persistent headache, and hemicrania continua. Four to 5% of the general population have primary chronic daily headache. Most chronic daily headache patients overuse analgesics or ergots. This article will consider recent insights into specific disorders, then psychiatric comorbidity, epidemiology, pathophysiology, and treatment.