Chronic migraine is an earlier stage of transformed migraine in adults

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.

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.

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.

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).

Chronic migraine is an earlier stage of transformed migraine.