Secondary headaches.

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.