Medication overuse headache in Spain.

EPIDEMIOLOGY AND DEMOGRAPHICS Spain has been a pioneer in the study of chronic daily headache (CDH) epidemiology. One of the main reasons for our interest in carrying out this kind of study is the way in which our health system is organized. In Spain > 95% of people only have public health insurance, and we all have one specific and stable family doctor in a Health Centre, a necessary intermediary for referral to a specialist in case of necessity. Therefore, it is easy to perform true epidemiological studies from Health Centres in such a country where people move infrequently. Almost a decade ago, we published the first CDH epidemiological study, in which we personally interviewed 1883 randomly selected subjects > 14 years old in the Health Centre of Camargo, in the region of Cantabria, in the north of Spain (1). CDH prevalence (according to Silberstein et al.’s criteria) was 4.7% (89 subjects). By diagnoses, 2.6% met chronic tension-type headache criteria, 2% transformed migraine criteria and only 0.1% had new daily persistent headache. These diagnoses were done after filling in a headache diary for 1 month and after examination and at least two interviews by a neurologist experienced in headache. Contrary to what happens in headache clinics, only a quarter of CDH subjects (22 of 89 subjects) met Silberstein et al.’s criteria, very similar to current International Headache Society (IHS) criteria, for overuse of symptomatic medication. Analgesic overuse was more frequent in those patients with transformed migraine (31%) compared with those with chronic tension-type headache (19%). Even though the numbers for the interviewed subjects were rather low to define prevalence, according to these data, prevalence of CDH with analgesic overuse or medication overuse headache (MOH) would be 1.3% of the general population. To better define the epidemiology of MOH we conducted a second survey with the same methodology (personal interview and diary for 1 month) in the Health Centre of Santoña in the same region. A total of 4855 unselected subjects were interviewed, using a quota sampling approach. Prevalence of MOH was 1.41%, confirming our previous results. Again, overuse was more frequent in migraineurs (prevalence 0.9%) than in subjects fulfilling chronic tension-type headache (0.4%) or new daily persistent headache criteria (0.1%) (Fig. 2). These data concur with those of other epidemiological studies and show that MOH is a common disorder in the general population. Quality of life was also assessed in this study by using the Short Form-36 Health Survey (SF-36) questionnaire. In the general population, MOH induces a remarkable decrease in all quality of life aspects studied by the SF-36 test, with Body pain and Role physical being the most affected items (2). General population data cannot necessarily be extrapolated to clinical practice. What is the ‘epidemiology’ of MOH in our neurological clinics in Spain? Headache is the most common reason for consultation, accounting for 24–32% of new neurological visits, according to two recent unpublished surveys among > 800 neurologists. Migraine is the most frequent diagnosis in our clinics, accounting for around half of consultations due to headache. In a very recent study, 13.5% of new out-patients attending a general neurological service in Spain had migraine (3). In our general neurological clinics, around 40–45% of migraine patients meet chronic migraine criteria. Of these, 30–70%, depending on the criteria and on the range of the hospital, overuse symptomatic medications. That means that MOH accounts for 2–5% of new consultations in general neurological services in our country. In our headache clinics, however, up to 40% of patients meet MOH criteria.