Clinical course in migraine: conceptualizing migraine transformation.

Migraine is currently conceptualized as a chronic disease with episodic manifestations, with attacks that increase in frequency in a subgroup (migraine transformation or progression). Transformation of migraine may be subdivided in three partially overlapping forms, although research in this area is still in infancy, and evidence is sometimes weak. Typically, transformation refers to increases in attack frequency over time leading to chronic migraine; this process is termed clinical transformation. Additionally, in some patients with migraine, physiologic changes in the CNS manifest themselves through alterations in nociceptive thresholds (allodynia) and alterations in pain pathways (physiologic transformation). Finally, in some individuals, definitive brain lesions including stroke and deep white matter lesions emerge (anatomic transformation). Herein we discuss the evidence that migraine may transform and then consider potential mechanisms as well as risk factors. We close with a brief discussion of clinical strategies that arise based on this perspective on migraine.