Chronic daily headache.

The term chronic daily headache (CDH) identifies a heterogeneous group of headaches characterized by the presence of daily or near-daily headache, including forms associated with medication overuse. This group includes chronic (transformed) migraine, chronic tension-type headache, new daily-persistent headache and hemicrania continua. According to population studies, CDH affects 4-5% of the general population worldwide, making it a significant social problem. CDH evolves from an episodic form of headache or, more rarely, is daily from onset. The classification of CDH continues to be debated, even though the recent revision of the diagnostic criteria for several primary headache forms seems to have resolved some of the nosographical difficulties. To date, no specific therapies have been approved for CDH and there have been few large-scale controlled trials of treatments in this area. This article reviews various aspects of CDH: classification issues, pathophysiological hypotheses and therapeutic (pharmacological and nonpharmacological) approaches.