Chronic Versus Episodic Migraine: The 15-day Threshold Does not Adequately Reflect Substantial Differences in Disability Across the Full Spectrum of Headache Frequency

Ryotaro Ishii MD, PhD; Todd J. Schwedt MD; Gina Dumkrieger PhD; Nim Lalvani MPH; Audrey Craven; Peter J. Goadsby MD, PhD; Richard B. Lipton MD; Jes Olesen MD; Stephen D. Silberstein MD; Mark J. Burish MD, PhD; David W. Dodick MD


Headache. 2021;61(7):992-1003. 

In This Article

Abstract and Introduction


Objective: To evaluate whether the 15-day threshold of headache days per month adequately reflects substantial differences in disability across the full spectrum of migraine.

Background: The monthly frequency of headache days defines migraine subtypes and has crucial implications for epidemiological and clinical research as well as access to care.

Methods: The patients with migraine (N = 836) who participated in the American Registry for Migraine Research, which is a multicenter, longitudinal patient registry, between February 2016 and March 2020, were divided into four groups based on monthly headache frequency: Group 1 (0–7 headache days/month, n = 286), Group 2 (8–14 headache days/month, n = 180), Group 3 (15–23 headache days/month, n = 153), Group 4 (≥24 headache days/month, n = 217). Disability (MIDAS), Pain intensity (NRS), Work Productivity and Activity Impairment (WPAI), Pain Interference (PROMIS-PI), Patient Health Questionnaire-4 (PHQ-4), and General Anxiety Disorder-7 (GAD-7) scores were compared.

Results: Mean (standard deviation [SD]) age was 46 (13) years (87.9% [735/836] female). The proportion of patients in each group was as follows: Group 1 (34.2% [286/836]), Group 2 (21.5% [180/836]), Group 3 (18.3% [153/836]), and Group 4 (26.0% [217/836]). There were significant relationships with increasing disability, lost productive time, and pain interference in higher headache frequency categories. There were no significant differences between Group 2 and Group 3 for most measures (NRS, all WPAI scores, PROMIS-PI, GAD-7, and PHQ-4), although MIDAS scores differed (median [interquartile range (IQR)]; 38 [20–58] vs. 55 [30–90], p < 0.001). Patients in Group 1 had significantly lower MIDAS (median [IQR];16 [7–30], p < 0.001), WPAI-% total active impairment (mean (SD): Group 1 [30.9 (26.8)] vs. Group 2 [39.2 (24.5), p = 0.017], vs. Group 3 [45.9 (24.1), p < 0.001], vs. Group 4 [55.3 (23.0), p < 0.001], and PROMIS-PI-T score (Group 1 [60.3 (7.3)] vs. Group 2 [62.6 (6.4), p = 0.008], vs. Group 3 [64.6 (5.6), p < 0.001], vs. Group 4 [66.8 (5.9), p < 0.001]) compared to all other groups. Patients in Group 4 had significantly higher MIDAS (median (IQR): Group 4 [90 (52–138)] vs. Group 1 [16 (7–30), p < 0.001], vs. Group 2 [38 (20–58), p < 0.001], vs. Group 3 [55 (30–90), p < 0.001], WPAI-%Presenteeism (Group 4 [50.4 (24.4)] vs. Group 1 [28.8 (24.9), p < 0.001], vs. Group 2 [34.9 (22.3), p < 0.001], vs. Group 3 [40.9 (22.3), p = 0.048], WPAI-% total work productivity impairment (Group 4 [55.9 (26.1)] vs. Group 1 [32.1 (37.6), p < 0.001], vs. Group 2 [38.3 (24.0), p < 0.001], vs. Group 3 [44.6 (24.4), p = 0.019]), and WPAI-%Total activity impairment (Group 4 [55.3 (23.0)] vs. Group 1 [30.9 (26.8), p < 0.001], vs. Group 2 [39.2 (24.5), p < 0.001], vs. Group 3 [45.9 (24.1), p = 0.025]) scores compared with all other groups.

Conclusion: Our data suggest that the use of a 15 headache day/month threshold to distinguish episodic and chronic migraine does not capture the burden of illness nor reflect the treatment needs of patients. These results have important implications for future refinements in the classification of migraine.


According to the International Classification of Headache Disorders, 3rd edition (ICHD-3), chronic migraine (CM) is defined by the presence of 15 or more headache days per month over the preceding 3 months, with at least 8 days per month meeting criteria for migraine.[1] Unlike other primary headache disorders that have chronic and episodic subgroups, ICHD-3 did not mention episodic migraine (EM), although this has been corrected by a glossary appendix[2] since clinicians use the term in practice and in publications. The headache frequency threshold of 15 days per month included in ICHD-3 was selected on an arbitrary basis by committee discussion to align with tension-type headache (Headache Classification Committee of the International Headache Society, Kyoto, Japan, 2005) and is a threshold that results in headaches being present on at least half of the month.[3]

CM prevalence as defined by ICHD-3 is estimated at 1.4%–2.2% among the general population.[4] Patients with CM have lower health-related quality of life, higher levels of disability, and a greater relative frequency of comorbid diseases compared with EM.[5–7] The EM and CM definitions allow for a wide range of headache frequencies within each subgroup, although the spectrum of disability within EM and CM subgroups has not been well characterized. Chalmer et al., in a headache center sample, reported that patients with EM who experienced 8–14 headache days per month are comparable to patients with CM with regard to disability and suggested classifying CM as ≥8 migraine days per month (proposed CM), disregarding the need for ≥15 headache days per month.[8] Buse et al., in a population sample, reported directionally similar results.[9] Delineating the relationships among monthly headache day categories and patient-reported outcomes such as disability, lost productivity, and pain interference could provide an empirical basis for determining treatment needs and examining the issue of subtyping migraine.

Our study compared the degree of migraine burden in four headache frequency subgroups: Group 1 defined as 0–7 headache days per month; Group 2 defined as 8–14 headache days per month; Group 3 defined as 15–23 headache days per month; and Group 4 defined as 24 or more headache days per month. We compared the relationship of headache frequency with sociodemographic characteristics, headache-related disability, headache-related work impairment, and symptoms of depression and anxiety. The main hypothesis was that the patients in Group 2 have a relatively high disease severity and burden. We did not use the terms EM and CM in our categorization because of our interest in exploring the empirical basis for this taxonomy.