In the simplest of terms, Chronic Migraine is Migraine or Headache occurring 15 or more days a month, at least eight of which must have Migraine symptoms. People living with Chronic Migraine have a Migraine or Headache more often than not.
When diagnosing and classifying types of Migraine and other Headache disorders, there’s a set of recognized criteria and classifications that are generally followed, a “gold standard.” In the field of “Headache medicine,” that gold standard is the International Headache Society’s (IHS) International Classification of Headache Disorders, now in it’s 3rd Edition (ICHD-3).
As research studies and clinical trials are designed, medications are submitted to the FDA for approval for use in the treatment of Migraine, and other issues arise, we’re seeing that chronic forms of Migraine often respond differently to treatment than episodic Migraine, patient needs are different, and that there are many reasons to standardize criteria for classifying Migraine as chronic.
Chronic Migraine was not addressed in the first edition of the ICHD, which was released in 1988. In 2004, Chronic Migraine appeared in the ICHD-II as a “complication of Migraine.” The description and criteria were brief. It was described as “migraine headache occurring on 15 or more days per month for more than three months in the absence of medication overuse.” The criteria were simple. Chronic Migraine had to have Headache fulfilling the criteria for Migraine without Aura on 15 or more days per month for three months and could not be attributed to another disorder.
Finally, in ICHD-3, Chronic Migraine is fully recognized with the following criteria:
1.3 Chronic migraine
Headache occurring on 15 or more days/month for more than three months, which, on at least eight days/month, has the features of migraine headache.
- Headache (migraine-like or tension-type-like1) on 15 days/month for >3 months, and fulfilling criteria B and C
- Occurring in a patient who has had at least five attacks fulfilling criteria B–D for 1.1 Migraine without aura and/or criteria B and C for 1.2 Migraine with aura
- On 8 days/month for >3 months, fulfilling any of the following:2
- Not better accounted for by another ICHD-3 diagnosis.3–5
- The reason for singling out 1.3 Chronic migraine from types of episodic migraine is that it is impossible to distinguish the individual episodes of headache in patients with such frequent or continuous headaches. In fact, the characteristics of the headache may change not only from day to day but even within the same day. Such patients are extremely difficult to keep medication-free in order to observe the natural history of the headache. In this situation, attacks with and those without aura are both counted, as are both migraine-like and tension-type-like headaches (but not secondary headaches).
- Characterization of frequently recurring headache generally requires a headache diary to record information on pain and associated symptoms day by day for at least one month.
- Because tension-type-like headache is within the diagnostic criteria for 1.3 Chronic migraine, this diagnosis excludes the diagnosis of 2. Tension-type headache or its types.
- 4.10 New daily persistent headache may have features suggestive of 1.3 Chronic migraine. The latter disorder evolves over time from 1.1 Migraine without aura and/ or 1.2 Migraine with aura; therefore, when these criteria A–C are fulfilled by headache that, unambiguously, is daily and unremitting from <24 hours after its first onset, code as 4.10 New daily persistent headache. When the manner of onset is not remembered or is otherwise uncertain, code as 1.3 Chronic migraine.
- The most common cause of symptoms suggestive of chronic migraine is medication overuse, as defined under 8.2 Medication-overuse headache. Around 50% of patients apparently with 1.3 Chronic migraine revert to an episodic migraine type after drug withdrawal; such patients are in a sense wrongly diagnosed as 1.3 Chronic migraine. Equally, many patients apparently overusing medication do not improve after drug withdrawal; the diagnosis of 8.2 Medication-overuse headache may be inappropriate for these (assuming that chronicity induced by drug overuse is always reversible). For these reasons, and because of the general rule to apply all relevant diagnoses, patients meeting criteria for 1.3 Chronic migraine and for 8.2 Medication-overuse headache should be coded for both. After drug withdrawal, migraine will either revert to an episodic type or remain chronic, and should be re-diagnosed accordingly; in the latter case, the diagnosis of 8.2 Medication-overuse headache may be rescinded.
Summary and Implications for Patients:
Despite the confusion, it’s safe to say that Migraine is considered chronic when patients have 15 or more Migraine or Headache days per month, eight of which must be Migraine.
Patients who are diagnosed with CM should still know what form or forms of Migraine they have — Migraine with Aura, Migraine without Aura, etc. You can find a full listing of the types and subtypes of Migraine in Detailing and Delving into the Types of Migraine.
- Headache Classification Committee of the International Headache Society. “The International Classification of Headache Disorders, 2nd Edition.” Cephalalgia 24 (s1). doi: 10.1111/j. 1468-2982.2003.00824.x
- Headache Classification Committee of the International Headache Society. “The International Classification of Headache Disorders, 3rd Edition (ICHD-3). Cephalalgia, Volume: 38 issue: 1, page(s): 1-211.