Headache is a common type of recurrent pain and one of the most frequent symptoms in neurology. Although virtually everyone gets occasional headaches, there are well-defined headache disorders that vary in incidence, prevalence, and duration (Robbins and Lipton 2010).
Before 1988, the headache classification systems that were available did not have clear operational rules, and nomenclature varied widely. In 1988, the International Headache Society instituted a classification system that has become the standard for headache diagnosis and, particularly, for clinical research (Headache Classification Committee of the International Headache Society 1988). The 2nd edition of the International Classification of Headache Disorders (ICHD-2) was released in September of 2004 (Headache Classification Committee of the International Headache Society 2004). According to this system, headaches are divided into 2 broad categories: primary headache disorders and secondary headache disorders. In secondary disorders, headaches are attributed to another condition, such as a brain tumor, infection, or head injury; for the primary disorders, no specific cause can be found.
Headache is the chief complaint of about 2% of patients who visit emergency departments in the United States (Goldstein et al 2006). Internists and neurologists are often called to evaluate, or are consulted by, patients during a headache attack. The diagnosis of acute headache is challenging and should proceed in an orderly fashion. Crucial elements include a thorough history, supplemented by general medical and neurologic examinations, and laboratory testing and neuroimaging of selected patients.