The 15-Day Threshold Does Not Adequately Distinguish Between Episodic and Chronic Migraines

Woman with headache, computer illustration.
The researchers’ goal was to evaluate whether the 15-day threshold of headache days per month reflects significant differences in disability across the migraine and its spectrum.

The use of a 15-headache day/month threshold in order to distinguish episodic and chronic migraine does not reflect the impact and burden of migraine nor the treatment needed of patients, according to research results published in the Headache: The Journal of Head and Face Pain.

During February 2016 and March 2020, the American Registry for Migraine Research (ARMR) had 1912 patients with a migraine diagnosis complete baseline questionnaires. Following the headache diagnosis, patients with additional diagnoses, such as hemiplegic migraine, were excluded due to having expected headache disability independent of the study’s variables that would affect the results.

The study resulted in having 836 patients (87.9% women, 91.4% White, mean age was 46 years) who were divided into 4 subgroups that were based on monthly headache frequency. The 4 groups were: 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).

Within the study, scores on 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) were compared.

When comparing the burden of migraine and psychiatric comorbidities with headache frequencies, there were significant differences between the subgroups. The median MIDAS scores were 16 in group 1, 38 in group 2, 55 in group 3, and 90 in group 4 (P< 0.001). With NRS, there were no differences among the 4 groups, with a median pain intensity of 6 (P=0.870). Among the results for GAD-7, groups 2 and 3 were slightly higher compared with group 1, but group 4 was significantly higher.

When answering questions about WPAI, only 477 out of the 486 patients who reported having a full time or part-time job answered. It is important to note headache frequency’s effect on WPAI is underestimated because patients within group 4 were less likely to have full or part-time jobs.

Participants were asked about absenteeism, presenteeism, total work productivity impairment, and total activity impairment. These variables were measured using the Kruskal-Wallis test and for comparing each of the headache frequency groups, the Steel-Dwass test was performed.

Within group 1, individuals had 32.1% total work productivity impairment and 30.9% total activity impairment, which was significantly lower compared with the other groups. Like the previous questions, group 2 and group 3 shared similar results for all four of the WPAI scores (P≤0.001). For the PROMIS-PI-T scores, group 4 scores were significantly higher, indicating high pain interference and group 1 scores were significantly lower. Groups 2 and 3 scores showed no significant difference (P=0.057).

Study limitations include lack of diversity due to a majority of the patients enrolled being White, female, and having a college education or higher and a potential underestimation of headache frequency of WPAI.

Overall, future research is encouraged in order to investigate all headache frequency thresholds to provide more meaningful subclassifications.

“These results suggest that using a threshold of eight headache days per month better reflects the impact and burden of migraine,” the researchers concluded. “Future research is needed to refine the headache day threshold that represents the most accurate inflection point where disability and disease burden increase significantly.”


Ishii R, Schwedt TJ, Dumkrieger G, et al. Chronic versus episodic migraine: the 15-day threshold does not adequately reflect substantial differences in disability across the full spectrum of headache frequency. Headache. Published online June 3, 2021. doi:10.1111/head.14154