Migraine chronification--concept and risk factors.

Migraine is a chronic disease with episodic attacks and a variable prognosis. In a subgroup, migraine evolves into a more protracted condition (migraine transformation or progression). Transformation of migraine may be subdivided into three partially overlapping forms. Clinical transformation describes the evolution from episodic into chronic migraine. Physiological transformation refers to alterations in nociceptive thresholds and in pain pathways that precede or accompany clinical transformation. Anatomical transformation refers to the emergence of definitive brain lesions (e.g., stroke and deep white matter lesions) in some migraineurs. Herein we conceptualize migraine as a progressive disease and discuss risk factors for transformation.