Serrano D, et al. - Among individuals meeting criteria for episodic migraine (EM) and chronic migraine (CM) at baseline, researchers looked for natural fluctuations in self-reported headache frequency as well as the stability and variation in migraine type. During follow-up at three-month intervals, they noticed a high level of short-term variability in headache days per month. As a consequence, the CM diagnostic boundary of ≥15 headache days per month was crossed by many individuals. Over the course of a year, nearly three-quarters of persons with CM at baseline drop below this diagnostic boundary at least once. Findings seemed significant for headache classification and diagnosis, the design and interpretation of epidemiologic and clinical studies, and clinical management.