ABSTRACT
The classification of very frequent primary headache disorders and the appropriate use of the term 'chronic daily headache' (CDH) are still controversial. Patients with CDH are difficult to classify using the current International Headache Society (IHS) classification system. Causes of short-duration CDH include chronic cluster headache, paroxysmal hemicrania (PH), short-lasting uni-lateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT), hypnic headache, idiopathic stabbing headache, and the cranial neuralgias. Patients with chronic migraine (CM) often have a past history of episodic migraine beginning in their teens or twenties. Although migraine transformation most often develops with medication overuse, transformation may occur without overuse. Hemicrania continua (HC), a unilateral, continuous, indomethacin-responsive headache with periodic exacerbations, was believed to be a rare disorder. Since CM evolves from migraine, one would also expect psychiatric comorbidity in CM. The biological relationship of migraine vulnerability to rebound headache and psychiatric comorbidity remains to be clarified.
