Abstract
Dear Sir Thanks to Dr Solomon for his interest in the revised criteria for chronic migraine. Dr Solomon was one of the highly treasured contributors to the first edition of The International Headache Classification, and his questions in this letter are very well focused.
The term chronic migraine was chosen because it is a parallel to chronic tension-type headache and chronic cluster headache and also because the term transformed migraine was considered to be too unclear, having many different meanings. Patients who have tension-type headache should still have the diagnosis chronic tension-type headache except when they have a lot of migraine. As usual in classification, it is debatable where to put the cut-off. We have decided to put it at eight migraine days a month because then the majority of the requested 15 days of headache a month would be migraine. Even if patients have a daily headache plus eight migraine attacks, they would still have the diagnosis chronic migraine. When patients have very frequent migraine, some of the apparent tension-type headaches are likely to be mild migraine attacks.
Criterion B requires attacks that fulfil all of the criteria for migraine without aura. This is necessary because, in counting the above-mentioned eight migraine days a month, we have abstained from the criterion of duration due to the chronicity of the disorder and we have accepted attacks that are treated so early that the full symptoms do not manifest. This brings us to the question about criterion C2. When patients have infrequent migraine, we request that they should fulfil the full set of criteria either by not treating certain attacks or by taking ineffective treatment. However, with frequent and possible chronic migraine attacks it becomes necessary to estimate the number of migraine attacks per month. This would make it necessary to keep patients medication free for 3 months, which is not possible. We have therefore accepted that attacks aborted by early specific treatment shall be counted as migraine.
Regarding the last question, my answer is less certain. It is clear that patients with chronic migraine and exclusively aura attacks do not exist or are exceedingly rare. However, if a patient has a mixture of migraine with and without aura, then also the aura attacks should count. This should be clearly stated in a future ICHD-2R.
The reason that we do not like the term chronic daily headache is because most experts teach that this is not a diagnosis. It is just a term for bad and frequent headaches. The use of chronic daily headache should always be accompanied by one or more specific diagnoses.
The subclassification suggested in the table is not useful. How does it distinguish between chronic migraine with tension-type headache and chronic tension-type headache with migraine? That question alone should be enough to demonstrate the inconsistency of the proposed of subclassification.