Chronic daily headache.

Chronic daily headache represents a range of disorders characterized by the occurrence of long-duration headache 15 or more days per month. The classification of these disorders continues to undergo revision to make them more clinically relevant, such as that which has been most controversial, the classification of chronic migraine. The role of medication overuse in what has commonly been known as rebound headache can have a significant influence on these disorders. The diagnosis of the chronic daily headaches, including chronic migraine and chronic tension-type headache, truly cannot be made if patients are having medication-overuse headache. This article reviews the criteria for medication-overuse headache and the subset of headaches making up chronic daily headache, as well as the epidemiologic and therapeutic aspects of these disorders.