[Clinical features and mechanisms of chronic migraine and medication-overuse headache].

Chronification of migraine headaches is one of the most urgent issues. Chronic migraine (CM) and medication overuse headache (MOH) are defined in international classification of headache disorders II (ICHD-II). Appendix criteria of CM and MOH were submitted and will take over the original criteria. I described a case of CM and a case of MOH. Here I pointed out some practical issues in diagnosis of CM or MOH. 1) It is not easy to define the association of headache worsening and the beginning of medication overuse in many cases. 2) Some patients cannot discontinue the overused drugs; therefore, the diagnosis of CM nor MOH cannot be completed. 3) Some patients are not released from their headache even after the discontinuation of drug. In these cases, there are two possibilities. As a result of CM, the patient had simply overused the ineffective medications. From another point of view, MOH caused irreversible brain changes and MOH do not disappear after the detoxification. 4) In a practical management, we often prescribe preventive medications simultaneously at the beginning of detoxification. In these cases, it is unclear which one of the detoxification or the preventive medication contributes the improvement of headache. The chronification of migraine is regarded as chronification of acute mechanism of migraine, i.e., inflammation of the trigeminovascular system and sensitization of the brain. Apart from medication overuse, there have been reported some new risk factors for migraine chronification, including frequent headache, female sex, obesity, low income, low education, stress by life events, depression, snoring, sleep disorders, and past history of neck or head injury. Chronification of migraine severely disturbs the quality of patient's life. More attention should be paid and the further and extensive studies are urgently necessary.