Disease classifications and their diagnostic criteria are often received with scepticism by the medical community and may not be put to extensive use. It has therefore been a pleasant surprise to see how well the first edition of The International Classification of Headache Disorders was received. It was accepted virtually immediately throughout the world for scientific purposes. Thus, the big wave of triptan studies were all performed in patients diagnosed according to this classification. Slowly but surely the principles of the classification have also altered clinical practice. Many questions not needed in order to classify primary headaches are no longer being asked in clinical interviews and, conversely, new criteria such as aggravation by physical activity are gradually being put to use in daily practice. The classification has been translated into more than 20 different languages and is thus available to the majority of doctors throughout the world.
When we published the first edition, we thought that a second edition of The International Classification of Headache Disorders would follow within five years because large parts of it were based on the opinion of experts rather than on published evidence. It took, however, 15 years until we now present the second edition and there are many good reasons for that. Relatively little criticism has prompted a revision. Nosographic research providing a better description of the clinical features of the different headache disorders has appeared only slowly and remains insufficient to allow a totally evidence-based classification. The world-wide dissemination of the English version of the first edition and the translation into more than 20 different languages has also taken much longer than we expected. Slowly, however, good suggestions for a revision accumulated and the epidemiological and nosographic knowledge increased to the extent where it became meaningful to start work on a second edition.
As for the first edition, I have also for this edition had the chairman's privilege of appointing the subcommittee members. Although the first committee did a fabulous job, it was my feeling that we should have a major replacement of membership in order to secure that the next generation of headache researchers be sufficiently represented. Consequently, the only members of the first committee who have also been members of the second are Giuseppe Nappi, James W Lance and I. We have been responsible for continuity. In appointing new members I have primarily paid attention to personal qualifications. Geographical representation and a wish to include persons with a well-argued critique against the first edition have also been taken into account. I am pleased to say that recruitment according to these principles proved successful. Every member has been vividly interested, outspoken and well-argued. Respecting the huge workload carried out by the first classification committee, the second committee openly debated any aspect of headache classification. Because of the meticulous work and the many fruitful discussions the second edition took much longer to do than any of us had expected. Every single set of criteria, every number and every word have been weighed carefully and tremendous effort and thought have been invested in the present publication. All the views of every member could not be taken into account, but every member has had considerable impact on the classification.
It is important for any field of medicine to have a generally-accepted classification that is used throughout the world. This is particularly true for headache as a young and developing field and because there is so much prejudice against headache disorders. Therefore, it is extremely important that the headache community at large and headache researchers in particular support the use of The International Classification of Headache Disorders, 2nd edition. No journal should publish papers related to headache that are not using or examining this classification and the associated diagnostic criteria. On the other hand, our intention is not to lock headache research into a rigid frame and we therefore issue a strong plea to the world's headache researchers to examine this second edition scientifically. In order to stimulate such studies, we have included an appendix which describes a number of orphan disorders that need validation. We also present a few alternative criteria that can be tested against the official ones.
I sincerely hope that this second edition of The International Classification of Headache Disorders will be received favourably by the headache community throughout the world and that it will be translated into even more languages than the first edition. Also, I hope that it will become a basis for world-wide teaching in headache classification and headache diagnosis and thereby benefit patient management. The International Headache Society works to improve the diagnosis, treatment and care of headache throughout the world. It also works to destigmatise headache sufferers and to gain recognition for these disorders as neurobiological conditions inflicting a very high burden on the sufferers and their relatives as well on society. It is imperative for the success of these efforts that researchers and clinicians as well as patients use the same diagnostic system and that this system is as precise as possible. This process was taken a long way by the first edition of The International Classification of Headache Disorders. The second edition will hopefully further promote unity in the way we classify, diagnose and treat headache patients throughout the world.