[Chronic migraine: clinical manifestations and differential diagnosis]

Chronic migraine is a condition that has been present since the dawn of medicine, although only recently has progress been made in characterising it nosologically. It is the result of the evolution of episodic migraine which, at one particular moment and in relation to certain risk factors, changes its characteristics. The diagnostic criteria of chronic migraine, which were initially very restrictive and based on the specific type of patient from the most important headache units, are gradually being adjusted to match the real situation experienced in most neurology departments. The consideration of medication abuse criteria has also evolved and this has made it possible to perform a prospective diagnosis of these cases, instead of requiring withdrawal from the abuse, which is not also feasible in practice. The influence of medication abuse in the development of chronic migraine remains a controversial issue. In our opinion, abuse is an important risk factor for the chronification of migraine, but it is not a necessary or a sufficient condition for it to become chronic. Like other authors, we recommend the use of the term 'chronic migraine' indistinctly for patients with or without abuse. The diagnosis of chronic migraine is not always a simple matter; the anamnesis is our best weapon, although in our patients with headache we must get used to taking into account not only the most striking bouts of pain but also the intercritical periods. The differential diagnosis has to be considered in cases of chronic headaches with prolonged episodes of pain. We draw special attention to its differentiation from tension-type headache and we recommend avoiding whenever possible the use of the term 'mixed headache'.