Treatment and outcome of chronic daily headache.

Chronic daily headache (CDH) refers to the daily or almost daily occurrence of headache for a prolonged period of time, with lack of a well-defined attack pattern. It constitutes the vast majority of daily headaches. Hemicrania continua, a condition that closely resembles CDH, will be discussed as part of this article because the two are difficult, if not impossible, to distinguish solely on the basis of their presentations.