Redefining chronic migraine: a matter for debate

The development and revision of chronic migraine criteria is driven by a desire to identify the most disabled segment of the patient population with the aim of improving patient outcomes. During the debate, Professor Dodick questioned whether the ICHD-3 defined 15-day threshold for chronic migraine (CM) adequately captures those with high burden of disease, or whether it unintentionally leaves some people behind and creates a disparity in headache care.

The ≥15-monthly headache day (MHD) threshold for chronic migraine is an artificial separator; redefining chronic migraine to include patients with ≥8 MHD many better serve all patients with high disease burden

New diagnostic criteria for chronic migraine are needed

To support his argument that new diagnostic criteria are needed for CM, Professor Dodick cited several studies that identify a group of patients with episodic migraine (EM) that are as disabled as patients with ICHD-3 defined CM.^1,2 The Chronic Migraine Epidemiology and Outcomes (CaMEO) study (N=16,789) found that substantial overlap exists between high frequency EM (HFEM; 8-14 migraine headache days [MHDs]) and low frequency CM (LFCM; 15-23 MHDs) in levels of moderate/severe disability, interictal burden, depression, and healthcare resource utilization.³

In addition, the American Migraine Prevalence and Prevention (AMPP) population-based study (N=11,603) demonstrated that respondents with HFEM (8-14 MHD) and CM (≥15 MHD) were remarkably similar on a broad range of variables including sociodemographics, disability/impact and comorbidities. There were many more significant differences between the HFEM and low (0-3 MHD) to moderate (4-7 MHD) frequency EM groups on the same variables.⁴

The subgroup of patients with CM has better access to care and therapies, and potentially there is a large subgroup of patients with high frequency EM who are currently underserved by medical care

Harold G. Wolff Award winning study

Dr Dodick also cited data from the seminal paper presented by Dr Ryotaro Ishii at #AHS2021, and winner of the Harold G. Wolff Award.⁵ In a study of the American Registry for Migraine Research (ARMR) (N=836), patients with migraine having 8-14 and 15-23 MHD had similar and substantial disease burden, impact on work productivity, and risk of moderate-severe symptoms of depression and anxiety.

In this paper, Ishii and colleagues concluded that use of a threshold of 15 days to divide patients with migraine into subgroups does not adequately capture the burden of illness or reflect the treatment needs of patients across the entire headache frequency spectrum. This leads to the conclusion that using a threshold of 8 MHD better reflects the impact and burden of migraine.

Chronic migraine is not a unique disease state

Migraine is a disease of many faces: both of patients and of the disease process whether it relates to the polygenic nature or multiple influences of the environment and of the genes

In counterargument, Professor Andrew Hershey, reasoned that CM is not a unique disease state but rather the current definition of CM is an artificial cut-off strictly limited by frequency (≥15 MHD). In real life, people with migraine fluctuate across the line of demarcation between EM and CM. Longitudinal analysis of the CaMEO study has shown that there is substantial variation in headache day frequency in people with EM and CM; transitions from EM to CM are common and nearly 75% of people with CM will remit to EM during a 12-month period.⁶

Keeping CM as a separate entity leads to the conclusion that there must be a ‘non-chronic’ version. The additional label of CM gives disease recognition, but also makes it more difficult for non-CM patients to gain access to some therapies.

Is migraine multiple disorders or a continuum?

The holy grail is to develop a personalized approach to care; this may be achieved by identifying endophenotypes or distinct patient subgroups based on frequency for now until we have a better means of differentiation, e.g., by finding a biomarker for aggressive disease

Professor Hershey explained that a better understanding of the migraine disease process with biomarkers and neuroimaging, and development of the phenotype of migraine as multiple different disorders accumulating together may give greater understanding than the current use of frequency as a biomarker allows. The future challenge is to identify specific biomarkers for different patient subgroups or show that migraine is a continuum.

In conclusion, Professors Dodick and Hershey agreed that the current threshold for CM of ≥15 MHD must go and should be reduced to ≥8 migraine headache days to encapsulate a greater proportion of patients with unmet treatment need and high disease burden.