Most simply stated, chronic daily headache (CDH) is headache, not Migraine, that occurs 15 or more days a month.
Doctors divide chronic daily headache into a number of subcategories:
Primary CDH: not attributable to an underlying disorder
Shorter than four hours duration
chronic cluster headache
chronic paroxysmal hemicrania
Longer than four hours duration
chronic tension-type headache
chronic Migraine (sometimes called transformed Migraine)
new daily persistent headache
Secondary CDH: attributable to an underlying disorder
Additionally, each of those types is typically subdivided into two groups: with and without medication overuse. This is because it has been found that rebound headaches, aka medication overuse headaches, often contribute to headache or Migraine becoming chronic. Interestingly, studies have shown that medication overuse is less common in patients who are treated by headache and Migraine specialists.
Studies have shown that
- CDH patients were more likely to snore and report problems with sleep than episodic headache and Migraine patients.
- Medication overuse is a factor in 80% of cases of chronic daily headache.
Studies of the populations of the U.S. and Europe have shown that 4-5% of the population have daily or nearly daily headaches or Migraines.
Silberstein, Stephen D.; Lipton, Richard B.; Goadsby, Peter J.; Smith, Robert T. "Headache in Primary Care." Isis Medical Media. 1999.
Young, William B.; Silberstein, Stephen D. "Migraine and Other Headaches." AAN Press. 2004.
Goadsby, Peter J.; Silberstein, Stephen D.; Dodick, David W. "Chronic Daily Headache for Clinicians." BC Decker Inc. 2005.