Proposal for a new classification of chronic headache.

Since the publication of the second edition of the International Classification of Headache Disorders (ICHD-2) in 2004, a fiery debate has been raging about chronic daily headache in general and about chronic migraine and medication overuse headache in particular. Based on a number of considerations and observations on the current state of knowledge, a proposal is advanced that suggests a few changes to ICHD-2, namely: (1) differentiation of migraine without aura at the second-digit level into infrequent, frequent and very frequent, based on frequency of attacks. (2) Inclusion of transformed migraine among the complications of migraine; this entry should be coded to 1.5.1 replacing chronic migraine and the only diagnostic criterion that needs to be changed over those already listed in the revised ICHD-2 (ICHD-2R) is its temporal pattern (more than 20 days/month for 1 year or more and never with more than 5 headache-free consecutive days). (3) Differentiation of transformed migraine at the fourth-digit level depending on the presence or absence of symptomatic medication overuse (i.e. use for more than 20 days/month) regardless of whether overuse played any role in the worsening of the headache. (4) Switching of medication overuse headache to the Appendix with other diagnostic criteria to be defined.