Chronic migraine is an earlier stage of transformed migraine in adults

BACKGROUND: Chronic migraine (CM) is characterized by 15 or more migraine days per month. Most adults with chronic daily headache (CDH) that evolved from migraine have < 15 days of migraine/month. They are often classified as transformed migraine (TM), a disorder not addressed in the International Headache Society classification. OBJECTIVE: To test the hypothesis that early in the course of migraine chronification, the frequency of migraine attacks is high and that as illness progresses the frequency of nonmigraine headaches increases. METHODS: Information was collected on 402 adults with TM and was divided into two groups. Group 1 TM had > or = 15 days of migraine/month, whereas Group 2 TM had < 15 days of migraine/month. Risk factors were modeled for number of migraine days per month using logistic regression. RESULTS: Of 402 subjects with TM, 121 (30.1%) were in Group 1. The proportion of Group 1 subjects decreased with age, from 71% below age 30 to 22% age 60 or above. The correspondent proportion of Group 2 increased from 29 to 78%. More than 15 days of migraine per month was independently predicted by younger ages (< 40 years; p = 0.002), shorter interval from episodic to CDH (< 5 years; p = 0.003), and shorter time since the development of CDH (< 6 years; p < 0.0001). CONCLUSION: Chronic migraine is an earlier stage of transformed migraine.