LAUSR

To the Editor: We thank Torres-Ferrus and Pozo-Rosich, Kuan-Po Peng et al., and Guglielmetti et al. for their interest in our study, Proposed new diagnostic criteria for chronic migraine (1) and for their thoughtful comments (2–4). We are pleased that Torres-Ferrus et al. (5) agree with us that the third edition of The International Classification of Headache Disorders (ICHD-3) criteria for chronic migraine (CM) (6) do not account for patients who have a high frequency of migraine, and a high level of suffering. Also, that it is time for a revaluation of the existing ICHD-3 criteria for CM. We are sorry that the important article by TorresFerrus et al. escaped our notice, since it is highly relevant and represents a major effort to analyse the concept of chronic migraine. Torres-Ferrus et al. show that high-frequency episodic migraine (HFEM) does not differ practically from CM but differs a lot from low-frequency episodic migraine, suggesting that HFEM and CM should be lumped in a future definition of CM. Our cut-off for HFEM was eight or more days of migraine per month for more than 3 months, while the cut-off of Torres-Ferrus et al. was 10 or more days of headache per month. Since they do not distinguish between headache days and migraine days, it is difficult to compare the number of days. Most likely their cut off corresponds to the one suggested by us, since some of their 10 days are likely not migraine but tension-type headache. Guglielmetti et al. have made some interesting points about public health considerations of widening the definition of chronic migraine, which we shall elaborate on later in this response. Based on our extensive, clinical semi-structured interview performed on all patients and the unique Danish registries, we showed that HFEM did not differ from CM with regard to demographic profile, migraine attack frequency, medication use, and social parameters, and the overall prevalence of comorbid diseases was similar in both groups. Furthermore, patients with HFEM purchased significantly more triptans than patients with CM. Finally, we found that the proposed new diagnostic criteria for CM doubled the number of patients with CM. These proportions were similar in a Russian population of medical students who had the same semi-structured interview as the Danish cohort.