A redefinition of primary headache: chronic migraine.

In the field of so-called chronic daily headache, it is not easy for migraine that worsens progressively until it becomes daily or almost daily to find a precise and universally recognized place within the current international headache classification systems. A proposal is advanced to differentiate between a form of high-frequency migraine without aura (10-20 days of headache per month for at least 3 months), to be considered as a migraine without aura subtype, and a form of transformed migraine (TM), to be considered as a complication of migraine. TM--a name that should be preferred to chronic migraine (CM)--would then replace the latter, from which it would distinguish itself by the more restrictive diagnostic criteria (at least 20 days of headache per month for at least 1 year, with no more than 5 consecutive days free of symptoms; same clinical features of migraine without aura for at least 10 of those 20 days).