From the Headache Diagnostic Laboratory (T.P.D., H.W.S.), Danish Headache Center and Department of Neurology (J.M.H.), Rigshospitalet-Glostrup, Faculty of Health Sciences, University of Copenhagen, Glostrup, Denmark; Department of Neurology (A.R., G.G.S.), Elisabeth-TweeSteden Hospital, Tilburg, the Netherlands; Department of Neurology (C.S.), Inselspital, Bern University Hospital, University of Bern, Switzerland; Department of Neurology and Anesthesiology/Critical Care Medicine (S.E.N.), Johns Hopkins University, Baltimore, MD; Center for Neurology (M.O.), Asklepios Hospitals Schildautal, Seesen; Department of Neurology (M.O.), University Hospital Essen, University of Duisburg-Essen, Germany; Neurometabolism (A.J.S.), Institute of Metabolism and Systems Research, College of Medical and Dental Sciences, University of Birmingham, UK; and Neurorehabilitation (A.R.G.), RehaClinic Bad Zurzach and University of Zürich, Switzerland. [Email]
A minority of headache patients have a secondary headache disorder. The medical literature presents and promotes red flags to increase the likelihood of identifying a secondary etiology. In this review, we aim to discuss the incidence and prevalence of secondary headaches as well as the data on sensitivity, specificity, and predictive value of red flags for secondary headaches. We review the following red flags: (1) systemic symptoms including fever; (2) neoplasm history; (3) neurologic deficit (including decreased consciousness); (4) sudden or abrupt onset; (5) older age (onset after 65 years); (6) pattern change or recent onset of new headache; (7) positional headache; (8) precipitated by sneezing, coughing, or exercise; (9) papilledema; (10) progressive headache and atypical presentations; (11) pregnancy or puerperium; (12) painful eye with autonomic features; (13) posttraumatic onset of headache; (14) pathology of the immune system such as HIV; (15) painkiller overuse or new drug at onset of headache. Using the systematic SNNOOP10 list to screen new headache patients will presumably increase the likelihood of detecting a secondary cause. The lack of prospective epidemiologic studies on red flags and the low incidence of many secondary headaches leave many questions unanswered and call for large prospective studies. A validated screening tool could reduce unneeded neuroimaging and costs.