BackgroundRelatively little is known about the stability of a diagnosis of episodic migraine (EM) or chronic migraine (CM) over time. This study examines natural fluctuations in self-reported headache frequency as well as the stability and variation in migraine type among individuals meeting criteria for EM and CM at baseline.MethodsThe Chronic Migraine Epidemiology and Outcomes (CaMEO) Study was a longitudinal survey of US adults with EM and CM identified by a web-questionnaire. A validated questionnaire was used to classify respondents with EM (<15 headache days/month) or CM (≥15 headache days/month) every three months for a total of five assessments. We described longitudinal persistence of baseline EM and CM classifications. In addition, we modelled longitudinal variation in headache day frequency per month using negative binomial repeated measures regression models (NBRMR).ResultsAmong the 5464 respondents with EM at baseline providing four or five waves of data, 5048 (92.4%) had EM in all waves and 416 (7.6%) had CM in at least one wave. Among 526 respondents with CM at baseline providing four or five waves of data, 140 (26.6%) had CM in every wave and 386 (73.4%) had EM for at least one wave. Individual plots revealed striking within-person variations in headache days per month. The NBRMR model revealed that the rate of headache days increased across waves of observation 19% more per wave for CM compared to EM (rate ratio [RR], 1.19; 95% CI, 1.13–1.26). After adjustment for covariates, the relative difference changed to a 26% increase per wave (RR, 1.26; 95% CI, 1.2–1.33).ConclusionsFollow-up at three-month intervals reveals a high level of short-term variability in headache days per month. As a consequence, many individuals cross the CM diagnostic boundary of ≥15 headache days per month.Nearly three quarters of persons with CM at baseline drop below this diagnostic boundary at least once over the course of a year. These findings are of interest in the consideration of headache classification and diagnosis, the design and interpretation of epidemiologic and clinical studies, and clinical management.Electronic supplementary materialThe online version of this article (doi:10.1186/s10194-017-0787-1) contains supplementary material, which is available to authorized users.

There are many people who experience headaches that are independent of illness, injury, or hangover. Approximately 4% of the population suffer from headaches on a daily or near-daily basis. It is apparent that patients with chronic daily headache in community samples differ in important ways from patients with chronic daily headache in subspecialty clinics. In this manuscript, we review clinic-based data on risk factors for chronic daily headache and summarize the current data on the epidemiology of chronic daily headache.

We conclude that a CER-ECD observational study that imposes no or minimal additional risk to or burden on patients may proceed ethically without express informed consent from participants in settings where: (a) patients are regularly informed of the health care institution's commitment to learning through the integration of research and practice; and (b) there are appropriate protections for patients' rights and interests. In addition, where (a) and (b) apply, some pragmatic, randomized trials that similarly impose no or minimal additional risk to or burden on patients may also proceed ethically without express consent, when certain additional conditions are satisfied, including: (c) the trial does not negatively affect patients' prospects for good clinical outcomes; (d) physicians have the option of using an intervention other than the one assigned if they believe doing so is important for a particular patient; and (e) the trial does not engage preferences or values that are meaningful to patients.

Internal consistency was >0.80 for the symptom severity and distress scales. All three scales showed stability over two weeks (ICC >0.70). Both validity hypotheses were supported. Comparison of effect sizes showed the GSAS is sensitive to changes in severity of symptoms. In conclusion, the GSAS is a reliable, valid, and responsive measure of GERD symptoms.