Classification of chronic daily headache by International Headache Society criteria: limits and new proposals.

We conducted a retrospective study of 150 patients with chronic daily headache (CDH) to determine how to categorize their headache according to the classification of the International Headache Society (IHS). All patients were first evaluated at Parma and Pavia Headache Centres (from January 1992 to March 1993) and had had headache for at least 15 days a month during the previous 6 months. Four patients were thereafter excluded due to poor reliability. The 146 patients who met our CDH criteria (92 with and 54 without clear-cut migraine attacks) could be classified into four groups: (i) chronic tension-type headache (CTTH)--27 patients; (ii) coexisting migraine plus CTTH--65 patients; (iii) unclassifiable daily headache--27 patients; and (iv) migraine and an unclassifiable interval headache--27 patients. Seventy-two percent of patients with CDH had migraine as the initial form of their headache. We therefore propose to revise the IHS classification for migraine, taking into account its evolution, and add two subcategories, migraine with interparoxysmal headache and chronic migraine.