Page 131 - The clinical aspects and management of chronic migraine Judith Anne Pijpers

Chronic migraine definition
As the clinical studies within this thesis embrace a time period from 2006 (chapter 3) to 2016 (chapter 4 – 6), different views and classifications on chronic migraine definitions have passed. Chronic migraine was first considered as a distinct entity in 2004, defined by the international Classification of Headache Disorders (ICHD) 2nd edition.1 In the following years, the definition of ≥15 migraine days per month appeared too restrictive and was loosened to ≥15 headache days per month, of which ≥8 migraine days (ICHD-2R, 2006).2 Diagnosis of a primary headache disorder, both (chronic) migraine or tension-type headache, could not be established in the light of concurrent medication overuse. In the most recent classifications, ICHD 3 beta, 20133 and subsequently ICHD-3, 20184, the latter was changed, such that the diagnoses of chronic migraine and medication overuse could co-occur. Complicating the classification by this co- occurrence is the circular reasoning in which a headache day is called a migraine day in case of triptan use. This is inevitable as intake of a triptan will prevent the evolution of migraine characteristics, but will also blur the diagnosis of CM in case of medication overuse.
Classifications can both have a clinical purpose, in which classification rules represent common phenotypes or indicated treatment, or a research purpose, ensuring homogenous subgroups.5,6 In the context of research, for which the ICHD was designed,5 a chronic migraine population in a clinical trial can now comprise patients with a primary headache disorder of migraine alone or a combination with tension-type headache in various frequencies, possible concomitant with a secondary headache due to medication overuse. In this case, the diagnosis chronic migraine might be inaccurate and only driven by a high and inappropriate triptan usage. Furthermore, chronic patients with medication overuse require a different treatment strategy as opposed to chronic migraine patients without medication overuse. This heterogeneity hampers appropriate population selections for clinical trials, and also hinders pathophysiological research. Whether or not a consequence of these limitations, the implementation of the ICHD criteria is falling short, as only 50% of clinical trials on chronic migraine use the correct criteria.7 Clinically, the discernment between episodic migraine and chronic migraine appears artificial. A recent study states that high-frequent episodic migraine (≥8 migraine days) is as disabling as chronic migraine, and should be included in revised criteria of
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Summary and general discussion
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