International Classification of Headache Disorders, Second Edition (ICHD-2): Current Status and Future Revisions

When the first edition of the International Headache Classification (ICHD-1) was published in 1988 (1), it was highly uncertain how it would be received by the clinical and the research community. Fortunately, it was rapidly accepted throughout the world, also by the World Health Organization (WHO), and its main principles were included in the International Classification of Diseases 10th version (ICD-10). When the International Classification of Headache Disorders, Second Edition (ICHD-2) was published in January 2004 (2), we knew that it would be an immediate success and would be put to generally use throughout the world. This has happened and, as of today, translations have been published in more than 15 languages, with more to come. There seems to be only one country in the world where the penetration of ICHD-2 is not completely successful. Unfortunately that country is also the world’s only superpower, the USA, where there are two main problem areas. One derives from the fact that the USA has never adopted ICD-10, which contains a much more modern headache classification than ICD8 and ICD9. In the latter documents, headache classification is obsolete, without detail, and tension-type headache, for example, is not identified as a specific neurological disorder. This means that reimbursement problems can be associated with the diagnosis of tension-type headache given by neurologists. Since most headache experts are neurologists, this may be one of the explanations for the relative lack of interest in tension-type headache in the USA. In contrast, industry and patients are very interested, as illustrated by the many TV advertisements recommending pain killers for headache. The other problem has been the diagnosis of chronic headache in patients that have a mixture of migraine and tension-typeheadache. ICHD-2 introduced a new entity: chronic migraine. However, it has been shown that the very strict diagnostic criteria of ICHD-2 include very few of the patients seen in tertiary headache centres. Therefore, new appendix criteria have relaxed the criteria for chronic migraine and for medication overuse headache. Research results, which have not yet been published, underlie these new appendix criteria. Classification research is much needed also to examine other parts of ICHD-2. In this issue of Cephalalgia, we have a fine example of such research in the paper by Marchioni et al. (3). They critically examine the chapter on: ‘Headache attributed to infection’ and suggest amendments. For experts who have not been a member of the Classification Committee or its subcommittees, it is of course difficult to imagine all the arguments behind ICHD-2. Any decision about suggestions such as those made in the paper by Marchioni et al. must therefore be discussed by the working party responsible for that chapter of the Classification and must also be endorsed by the main Committee. This having been said, my personal comments on the paper of Marchioni et al. are the following. 9.1. 2. ‘Headache attributed to lymphocytic meningitis’ should be renamed Headache attributed to nonbacterial lymphocytic meningitis because tuberculosis, as a bacterial infection, should belong under 9.1. 1 even though TB meningitis is monocytic. 9.1. 2 could be subdivided into acute and chronic at the fourth digit. The suggestion to include headache attributed to hyperthermia is interesting. However, it is not usual to suffer a headache in a sauna. Thus, it is uncertain whether hyperthermia without infection can cause headache. The comments about HIV and AIDS are well taken and the subcommittee would need to examine this carefully. The authors do not focus on the fact that HIV/AIDS is actually a virus infection and therefore could be placed as a subgroup at the fourth digit under headache attributed to systemic viral infection. A caveat to rule out headache caused by antiretroviral drugs might be appropriate, since presence of headache may dictate a change of drugs. The authors must do more research before suggesting dizziness and difficulty in concentrating as part of the criteria for 9.4. 1 chronic postbacterial meningitis headache. Certainly, aseptic meningitis