Epidemiology of headache.

This thesis is based on nine previously published papers. It represents the first prevalence study of specific headache entities in a representative general population, where the diagnoses are based on a structural interview and examination by a physician using internationally accepted operational diagnostic criteria. The study population was a random sample of 1000 men and women aged 25-64. The participation rate was 76%. The prevalences of the different forms of headache are assessed and the study provides descriptive data concerning symptomatology, precipitating factors, impact of female hormones, use of medical services and work consequences of the headache disorders and describes various factors associated with the disorders. Only half of migraineurs and one-sixth of subjects with tension-type headache consulted their general practitioner because of headache and even less consulted a specialist. These consultation rates reflect the selection of cases that may bias studies in clinic populations. The study supports the notion that migraine and tension-type headache are separate clinical entities and that migraine without aura and migraine with aura are distinct subforms of migraine. Migraine and tension-type headache are sex- and age-dependent disorders with female preponderance and lower prevalence in older age groups. The female preponderance may be explained by clinical factors related to female hormones. There is no clear evidence of any association between sociodemographic variables and migraine or tension-type headache. Tension-type headache is related to a series of psychosocial variables while migraine is not. The results suggest that migraine is primarily a constitutional disorder and tension-type headache a more complex phenomenon influenced by several psychosocial factors. The limitations of cross-sectional data in pointing out risk factors with sufficient certainty are stressed. Longitudinal follow-up studies are the most important challenge in future epidemiological headache research.