Chronic daily headache--one disease or two? Diagnostic role of serum ionized magnesium.

The entity of chronic daily headache (CDH) is well documented, but is not included in the current classification. We divided patients with CDH into groups with and without migrainous features. This division resulted in clearly distinguishable syndromes of daily migrainous headaches (DMH) and daily tension-type headaches (DTH). Family history of headaches was more common in patients with DMH. Patients in both groups had a high incidence of caffeine or drug overuse. The clinical division into DMH and DTH was supported by our finding of a higher incidence of disturbed magnesium (Mg) metabolism in patients with DMH. Of 26 patients with DMH, 8 (30.8%) had low serum ionized, but not total, Mg levels, and 16 (61.5%) had high ionized calcium/magnesium ratios. The corresponding numbers for the 22 patients with DTH were 1 (4.5%) and 8 (36.4%). These new laboratory measurements offer possible biological markers for the diagnosis of different headache syndromes.