Abstract
Dear Sir Sun-Edelstein and co-authors (1) are undoubtedly correct in declaring that controversy continues to exist with regard to the understanding and classification of chronic daily headaches, including chronic migraine (CM) and medication overuse (MOH) headache in the current International Classification of Headache Disorders (ICHD-II) (2), particularly regarding the suggestions for revision of MOH. I would like to make the following points in this respect:
Though obvious, it needs to be stressed that the diagnosis of MOH has a direct effect on the treatment of patients with frequent headache, through the fact that it can lead to a withdrawal (with-holding) of the therapy to relieve their pain. With-holding an effective therapy can only be ethically justified insofar as it contributes to the patient’s well-being. Otherwise, it would be seen as a denial of assistance. This over-riding well-being of the patient was taken into account in the previous formulation of the MOH in ICHD-II through the fact that the discontinuation of a medicinal therapy is linked to the goal of improving the headache disorder in the form of the essential criterion that the ‘headache resolves or reverts to its previous pattern within 2 months after discontinuation of overused medication’ (2). According to Sun-Edelstein and colleagues, the revision suggestion of the Headache Classification Committee now stipulates that the ‘diagnosis [MOH] should be made in patients with primary headache and concurrent medication overuse’. The problem is shifted to the definition of the term ‘regular overuse’, as diagnosis criterion B is seen as fulfilled if there is ‘regular overuse for >3 months of one or more acute/symptomatic treatment drugs as defined under subforms’, i.e. according to the type of medication, use on ≥10 or ≥15 days/month. Irrespective of the fact that this distinction was expressly not made on the basis of reliable data (‘expert opinion rather than formal evidence suggests that use on ≥15 days/month rather than ≥10 days/month is needed to induce analgesic-overuse headache’, as formulated in the ICHD-II 8.2.3), the consequence is that for all those patients for whom the diagnosis 8.2.7, of probable medication-overuse headache according to the ICHD-II applies, the diagnosis of MOH would be made following the revision. This would give rise to a huge increase in the number of these cases. However, the question is whether this would also be scientifically sound. How small the correspondence of the diagnoses can be for pMOH and MOH is shown by a new clinical case series (3), in which from the original 80 patients with pMOH, after a withdrawal treatment, only one-third (n = 27) ultimately had a genuine MOH after 3 months. In a further clinical case series with 215 patients with pMOH, the diagnosis of MOH was confirmed in accordance with ICHD-II only for somewhat more than half (n = 127) (4). It is overlooked that it can be difficult to decide whether the regular overuse of pain medication is the cause or the result of the increased headache frequency (5). It is well known that correlation does not justify causation, and one can only agree with Maizels and Burchette (6) when they state that ‘an important caveat is that patients with medication overuse should not be labelled as having ‘medication-induced headache’ or ‘drug-rebound headache’ without careful clinical evaluation, including documentation that the headache resolves with withdrawal of the medications. Medication induced headache implies that the frequent use of medication is the cause of the headache, whereas medication overuse may be the result of on unrecognised, potentially worrisome headache or inadequate treatment of a primary headache disorder, or as Ward (7) puts it: ‘medication overuse may be a consequence of (frequent) headache or a cause of it’. In their significant article on the reformulation of MOH, Ferrari et al. (8) point out that, in such a complex disorder as MOH, it is difficult to obtain a classification that is both easily applicable and unambiguous. Although, according to their evaluation, the latest revision is more applicable to clinical reality, it is unlikely to allow rigorous research and progress in the understanding of its basic mechanisms and/or progress in its treatment. They, therefore, propose to use the diagnosis of probable MOH for research aims and to reclassify MOH subforms according to the presence or absence of a dependence-producing property of overused drugs. Subform 8.2.2 (analgesic abuse headache) would incorporate, in the same category (analgesics), drugs belonging to completely different classes, for example, aspirin, mild analgesics, barbiturates, other non-narcotic compounds, and narcotic analgesics. This would not be very correct from a pharmacological perspective. It would ignore the fundamental differences in the mechanism and spectrum of action of different medications and, in the opinion of Ferrari et al., (8) it has not contributed at all to their role in inducing MOH. These points, which I would like to expressly agree with, surprisingly remain completely unconsidered in the revision suggestions put forward so far.
For these reasons, it is difficult to support the strong proposals of Sun-Edelstein and co-authors to adopt the changes delineated in ICHD-IIR for the diagnosis of CM and MOH immediately. It is to be hoped that, prior to the publication of the revision of the ICHD-II, on the basis of a broader discussion, the suggestions of Ferrari et al., (8) among others, will be taken into account.