The convergence hypothesis.

The Convergence Hypothesis postulates a single pathophysiological mechanism to explain the clinical spectrum of primary headaches seen in patients with migraine. The history and the scientific underpinnings of the Convergence Hypothesis are presented. Extrapolations from the Convergence Hypothesis are used to explore the evolution of episodic to chronic migraine and the development of common migraine co-morbidities as a consequence of frequent migraine. A patient staging system is presented to illustrate this transformation process in migraine patients.