Chronic migraine: Diagnosis based on its temporal progression
When the International Headache Society published the first edition of the International Classification of Headache Disorders (ICHD-I) in 1988, chronic migraine . Migraine was classified as an episodic headache disorder. A subtype of migraine that occurs daily or almost daily was not defined. However, the ICHD-I did include a for medication-induced headache . The diagnostic criteria for such a disorder required headaches on at least 15 days per month with daily use of a specific minimum dose of the substance for more than three months and remission of the headache within one month of substance withdrawal. The diagnosis could only be made after successful withdrawal from the substance. Finally, the ICHD-I defined a second type of chronic headache: tension-type headache . The ICHD-I classification principle envisioned multiple diagnoses differentiating between various headache disorders, which were intended to form the basis for targeted treatment. A typical patient in a headache specialist clinic with daily headaches would then receive three diagnoses: migraine, chronic tension-type headache, and, before medication withdrawal treatment, a suspected diagnosis of medication-overuse headache.
A sub-differentiation into chronic migraine with at least 15 migraine days per month, not attributable to another disorder or medication overuse, was introduced in the 2004 second edition of the ICHD-II. Simultaneously, the concept of chronic daily headache or transformed migraine gained traction in the USA. The latter diagnosis describes the transition from an episodic to a chronic form of migraine – independent of medication overuse. A globally accepted consensus on a uniform diagnosis for chronic migraine and medication-overuse headache is still lacking. An overview of the ongoing development of definitions, classifications, and diagnostics for these conditions over the past decade can be found here:
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