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The international classification of headache disorders (ICHD) was first published in 1988 and updated in 2003. An updated version (ICHD Beta 3) was published in 2013 as a document open for comment (see Annex 2).5
Migraine is subdivided into migraine with and without aura. It is defined as episodic and chronic.
Episodic migraine
Episodic migraine occurs on less than 15 days per month and can be further subdivided into low frequency (1–9 days per month) and high frequency (10–14 days per month).5
Chronic migraine
Chronic migraine occurs on 15 or more days per month.5 In the first two versions of ICHD patients had to have 15 or more migraines per month. This group of patients is very small and it was increasingly recognised that this definition did not represent the majority of patients with chronic headache evolving from episodic migraine. The majority of patients with chronic migraine have background headache with superimposed migraine attacks. A consensus statement was produced in 2007 with a new definition of chronic migraine and this has been used in all subsequent studies on chronic migraine.16 Chronic migraine is now defined as headache on 15 or more days per month with superimposed migraine on eight or more days per month, for more than three months. This has been further refined in the ICHD beta 3 edition to allow migraine attacks to be with and without aura and also to include attacks that the patient believes are migraine and respond to acute treatment for migraine.5
Medication-overuse headache is defined as headache on 15 or more days per month that has evolved along with the frequent use of acute medication, for more than three months.5 In the majority of patients this is a complication of migraine and patients with MOH often have a chronic migraine pattern (see section 5). Importantly, not all patients with chronic migraine frequently using acute treatment have MOH; some have poorly-treated migraine. For triptans, opioids and combination analgesics 10 or more days use per month is considered sufficient to cause MOH, and for simple analgesics (for example, aspirin, ibuprofen and paracetamol) 15 days per month.5 When prescribing acute treatment for migraine, patients should be counselled about the risk of MOH.
The majority of studies in this guideline use the ICHD-2 2003 definitions except for those on chronic migraine where the 2007 consensus statement is used.
The ICHD Beta 3 diagnostic criteria for migraine and MOH are listed in Annex 2.