Page 19 - The clinical aspects and management of chronic migraine Judith Anne Pijpers

and the locus coeruleus (Figure 1).1 The involvement of the descending pain modulating pathway specifically in migraine chronification has been suggested by functional-MRI studies. Differences in functional connectivity within this network have been found between allodynic and non-allodynic patients. In this study, allodynia patients had a higher attack frequency compared to non-allodynia patients, so the comparison might be extended to chronic migraine versus episodic migraine.26 Moreover, a study in chronic and episodic migraine patients suggests that the posterior part of the hypothalamus might be involved in experiencing migraine pain in general, and the anterior part in migraine attack generation, and consequently chronicity.27 Therefore, migraine chronification could be further enhanced by alterations in the descending pain modulating pathways, resulting in a lack of pain inhibition.
Risk factors for chronic migraine
Over the years, many factors for migraine chronification have been studied, resulting in several factors that consistently increase the risk for chronic migraine. Besides a high baseline headache frequency (which assumedly indicates that the transformation progress has already been initiated), overuse of acute headache medication, depression, and allodynia are important independent risk factors.10,24,28–30 Genetic factors have also been suggestive to increase susceptibility for migraine chronification.31
Medication overuse
Overuse, or high-frequent use, of acute pain medication is a major risk factor for chronic migraine.10,29,30 Medication overuse is defined as use of analgesics on at least 15 days per month, or use of either triptans or combinations of acute pain medication on at least 10 days per month (box 2).3 The relation between medication overuse and chronic migraine gives rise to questions on the direction of the association: does medication overuse really lead to more migraine, or do patients simply use a lot of medication because of the increasing frequency of headache? A number of studies suggest the first option, that frequent medication overuse in itself causes migraine chronification. Firstly, the relationship has been suggested by the temporal relationship in the longitudinal studies identifying medication overuse as a risk factor, adjusting
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General introduction
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