Classification and epidemiology of headache.

Headache disorders are remarkably common. Like back pain, headache is a symptom that has a broad range of possible causes. Diagnosis of primary headache disorders (migraine, tension-type headache, cluster headache) depends on systematic exclusion of secondary disorders and systematic identification of the specific features of the primary disorders. Thus, migraine should be viewed as an episodic syndrome of pain, involving intracranial structures associated with other neurologic disturbances. Because of the large number of potential etiologies, clinicians must approach headache classification systematically. In this chapter, we provide an overview of headache classification followed by discussions of epidemiology.