Transformed migraine, analgesic rebound, and other chronic daily headaches.

Although the International Headache Society's classification of headache has greatly enhanced the diagnosis of migraine and cluster headache, its application in chronic headache has been less than satisfactory. Based on a review of the literature and the author's experience, this article demonstrates the need for an expanded and modified classification and broader understanding of chronic headaches. The author proposes new categories, including transformed migraine. Analgesic rebound is described as a major cause of chronic headaches. The comorbidity of chronic headache disorders is also discussed. The article concludes with a suggestion for management of chronic headaches.