Purpose of review: This article identifies the pertinent historical issues that lead to the identification of those headaches needing additional testing to exclude a serious underlying cause.
Recent findings: Recurrences of giant cell arteritis, even after presumed successful treatment, are common. Postural orthostatic tachycardia syndrome is an often unrecognized cause of headache.
Summary: Patients with a primary headache disorder are more susceptible to the development of headache when a secondary cause occurs. Their headaches may be phenotypically similar to their primary headache disorder. Therefore, a secondary cause should be considered in patients with preexisting headache disorders who develop a significant increase in the number and severity of those attacks.