Epidemiology of chronic daily headache.

Daily or near-daily headache is a widespread problem in clinical practice. The general term of chronic daily headache (CDH) encompasses those primary headaches presenting more than 15 days per month and lasting more than 4 hours per day. CDH includes transformed migraine (TM), chronic tension-type headache (CTTH), new daily persistent headache (NDPH), and hemicrania continua (HC). Around 40% of patients attending a specialized headache clinic meet CDH diagnostic criteria, of which 80% are women. In these clinics about 60% of patients suffer from TM, 20% from CTTH, and 20% meet NDPH criteria. Most, some 80%, overuse symptomatic medications. One should be very cautious on extrapolating these numbers to the general population. CDH prevalence in the general population seems to be around 4% to 5% (up to 8% to 9% for women). Regarding the prevalence of CDH subtypes, NDPH is rare (0.1%), whereas the prevalence of TM (1.5% to 2%) and CTTH (2.5% to 3%) is clearly higher. In contrast to data from specialized clinics, only around a quarter of CDH subjects in the general population overuse analgesics; the prevalence of CDH subjects with analgesic overuse being 1.1% to 1.9% of the general population. Most of these patients with analgesic overuse are TM patients.