Red and orange flags for secondary headaches in clinical practice: SNNOOP10 list

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. Clinical experience or large case series form the basis for many red flags, which only allows for the sensitivity to be known. However, the specificity and predictive value are also important.
We aim to review the incidence and prevalence of secondary headaches and review literature that can contribute to the sensitivity, specificity and, if possible, predictive value of red flags in secondary headaches.
We review the following red flags: (1) systemic symptoms including fever; (2) neoplasm history; (3) neurological deficit (including lowered consciousness); (4) sudden or abrupt onset; (5) older age (onset after 50 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) post-traumatic onset of headache; (14) pathology of the immune system such as HIV; (15) painkiller abuse or recent change of medication.
Every new headache patient should be screened using this list of symptoms as this will likely increase the likelihood of detecting a secondary cause. A lack of prospective epidemiological studies on red flags leaves many questions unanswered. A next step forward would be large prospective studies given the low incidence of many secondary headaches. A validated screening tool could minimize the unneeded conduction of neuroimaging and costs. The presence of a checklist will lead to increased awareness and attention for secondary headaches.

Key Words: red flag, headache, imaging, sensitivity, specificity, predictive value