The International Headache Society classification of chronic daily and near-daily headaches: a critique of the criticism.

The classification of the International Headache Society (IHS) published in 1988 has been positively received throughout the world. However, the classification of headaches occurring daily or almost daily has been criticized repeatedly. This criticisim is discussed in the present review. It is possible to classify virtually all chronic headache patients using the IHS Classification and there seems to be more need for emphasizing a correct application of the classification than for a revision in this regard. The entity of transformed migraine is disputed and so is the existence of hemicrania continua. Neither of these syndromes has been adequately defined nor studied. Chronic daily headache of sudden onset (new persistent daily headache) is not adequately classified at present and should be included as a separate entity in the next edition of the IHS Classification. In a future revision it should also be possible to classify drug-related headache simply on the basis of drug consumption and without mandatory demands for withdrawal. Better longitudinal studies of patients with chronic daily headache are necessary to evaluate finally whether a revision of the classification of these headache syndromes is necessary. Eventually the ongoing discovery of migraine genes is likely to change radically the classification of migraine.