The criteria for chronic migraine (CM), as proposed by the Second Edition of the International Classification of Headache Disorders (ICHD-2) is very restrictive, excluding most patients that evolve from episodic migraine. In this study we empirically tested three recent proposals for revised criteria for CM. We included individuals with transformed migraine (TM) with or without medication overuse, according to the criteria proposed by Silberstein and Lipton. All individuals had headache calendars for at least three consecutive months. We assessed the proportion of subjects that fulfilled ICHD-2 criteria for CM or probable chronic migraine with probable medication overuse (CM+). We also tested three proposals for making the CM criteria more inclusive. In proposal 1, CM/CM +would require at least 15 days of migraine or probable migraine per month. Proposal 2 suggests that CM/CM +would be classified in those with ≥15 days of headache per month, where at least 50%of these days are migraine or probable migraine. Proposal 3 suggests that CM/CM +would be classified in those with chronic daily headache and at least 8 days of migraine or probable migraine per month. Among TM sufferers, 399 (62.5%) had TM with medication overuse, and just 10.2%were classified as CM+158 (37.5%) had TM without medication overuse; just nine (5.6%) met current ICHD-2 criteria for CM. Using the alternative criteria, proposal 1 included 48.7%of patients with TM without medication overuse; proposal 2 captured 88%, and proposal 3 classified 94.9%of these patients. For TM with medication overuse, the proportions for proposals 1-3 were, respectively, 37%, 81%and 91%. The differences were statistically significant, favouring proposal 3. Consistently, criteria for CM and CM+should be revised to require at least 8 days of migraine or probable migraine per month, in individuals with 15 or more days of headache per month.
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