Incidence and predictors for chronicity of headache in patients with episodic migraine

The authors followed 532 consecutive patients with episodic migraine (<15 days/month) for 1 year. Sixty-four patients (14%) developed chronic headache (≥15 days/month). The odds ratios for developing CH were 20.1 (95% CI 5.7 to 71.5) comparing patients with a critical (10 to 14 days/month) vs low (0 to 4 days/month) and 6.2 (95% CI 1.7 to 26.6) in patients with an intermediate (6 to 9 days/month) vs low headache frequency and 19.4 (95% CI 8.7 to 43.2) comparing patients with and without medication overuse.