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Fibromyalgia Among Patients With Chronic Migraine and Chronic Tension‐Type Headache: A Multicenter Prospective Cross‐Sectional Study: A Comment

After reading the article by Cho et al, we would like to congratulate the authors for such an interesting investigation, which allows the scientific community to expand knowledge on two complicated diseases: fibromyalgia and migraine. Most of the studies assessing fibromyalgia use the 1990 American College of Rheumatology (ACR) criteria. We consider it important to emphasize the fact that the authors used the 2010 American College of Rheumatology (ACR) diagnositc criteria, as well as the International Classification Headache Disorders-3 (ICHD-3) to diagnose migraine, which is a worldwide diagnostic criteria. Fibromyalgia and migraine are both very much related diseases and they are part of the “central sensitization syndrome.” The study by Cho et al is the first time these diseases have been assessed with two updated diagnostic instruments. For this reason, this investigation perhaps can be taken as a model for future studies, in order to improve our knowledge about these two complex diseases and an apparent association between each other. Nevertheless, we consider a few suggestions could be acknowledged. First, the inclusion criteria are not well defined. It is mentioned that, in order to be recruited, patients had to visit a neurology outpatient clinic for the first time in the case of headache; however, another criteria states: “diagnosis of chronic migraine or chronic tensionaltype headache based on the headache history during the previous year.” Also, there is no information about the number of people who were potentially eligible, those who declined to be included, those who were initially selected, nor about those who were abandoned after being recruited; in other words, it would be good that the authors show the flowchart of patients. Finally, in Cho et al’s table 2, “Widespread Pain Index of Participants With CM and CTTH,” they used chi-square to compare rates of prevalence, but not all of the results complied with the assumptions of this test, specifically the variable “frequency pain in the right jaw.” For that reason, it would be highly recommended for the authors to use the Fisher test instead. Likewise, for multivariate analysis, the odds ratio was calculated; however, due to the high prevalence of the outcome (66.9% for chronic migraine), it would have been more suitable to use the prevalence ratio (PR) with Poisson regression, in order to avoid the strength of the association being overestimated. Acknowledgment: Authors would like to thank Dr. German F. Alvarado for his advice during the development of this letter.