Chronic migraine: current pathophysiologic concepts as targets for treatment.

Chronic daily headache (CDH) affects approximately 4% of the population and exerts a significant degree of disability on its sufferers. Chronic migraine (CM) is a subset of CDH that represents migraine without aura occurring on 15 or more days per month for at least 3 months. Although numerous risk factors are associated with the development of CM, the pathophysiology governing its genesis is largely unknown. The role of neurotransmitters, such as glutamate, as well as disruptions of antinociceptive systems and structures, are implicated in CM and are supported by the fact that treatments targeting these abnormalities are effective.