Understanding the patient with migraine: the evolution from episodic headache to chronic neurologic disease.  A proposed classification of patients with headache. 
Traditionally, episodic primary headache disorders are characterized by a return of preheadache (normal) neurologic function between episodes of headache.  In contrast, patients with chronic headache often do not return to normal neurologic function between headache attacks.  This article proposes that the evolution from episodic migraine to chronic headache may parallel the neurologic disruption observed during the progression of an acute migraine attack and that changes in baseline neurologic function between episodes of headache may be a more sensitive indicator of headache transformation than headache frequency alone.  Early recognition of nonheadache changes in nervous system function may offer a more sensitive and specific approach to migraine prevention.