Red flags including sudden onset, high pain intensity, pattern of change of a preexisting headache, focal neurological signs or seizure, systemic signs and precipitation by physical activity can guide the clinician to suspect a secondary headache. (Wijeratne et al, 2023)
Red flag headache syndromes caused by life-threatening disease as well as symptomatic headaches requiring immediate treatment to prevent irreversible deficits need to be identified as soon as possible. Clinical signs and symptoms indicating a secondary headache syndrome are summarized in the so-called SNOOP list (SNOOP: systemic symptoms, neurological symptoms, acute onset, older patients, and previous history).
Various imaging and laboratory evaluations are indicated in the presence of any "red flag" signs or symptoms. Head CT is the procedure of choice for acute headache presentations, and brain MRI for those with chronic headache complaints. (Kaniecki & Levin 2019) Red flag signs and symptoms include focal neurologic signs, papilledema, neck stiffness, an immunocompromised state, sudden onset of the worst headache in the patient's life, personality changes, headache after trauma, and headache that is worse with exercise. If an intracranial hemorrhage is suspected, head computed tomography without contrast media is recommended. For most other dangerous causes of headache, magnetic resonance imaging or computed tomography is acceptable. (Hainer & Matheson 2013)
Examples of conditions which might produce red flag headaches are subarachnoid hemorrhage, reversible cerebral vasoconstriction syndrome, elevated intracranial pressure, hydrocephalus, cerebral venous sinus thrombosis, arterial dissection, central nervous system infection, and inflammatory vasculitis. (Kopel et al, 2021)
Thunderclap headaches live up to their name, striking suddenly like a clap of thunder. The pain of these severe headaches peaks within 60 seconds. Thunderclap headaches are uncommon, but they can warn of potentially life-threatening conditions — usually having to do with bleeding in and around the brain. Seek emergency medical attention for a thunderclap headache.
Thunderclap headache (TCH) is a common presentation in the emergency department and, although multiple causes have been described, subarachnoid hemorrhage (SAH) is the primary concern and early diagnosis is critical. CT is highly sensitive if performed within 6 hours of onset. Patients with aneurysmal or perimesencephalic SAH should be evaluated with CT angiography. Further work-up should be guided by the pattern of blood. Patients with negative CT angiography may be further evaluated with MR imaging, especially patients with peripheral convexity SAH. (Malhotra A, Wu X, Gandhi D, Sanelli P. The Patient with Thunderclap Headache. Neuroimaging Clin N Am. 2018 Aug;28(3):335-351. doi: 10.1016/j.nic.2018.03.002. Epub 2018 Jun 8. PMID: 30007749.)
Although the evaluation of TCH is exhaustive, the potentially catastrophic consequence of a missed diagnosis of sentinel headache justifies the efforts. (Chen CY, Fuh JL. Evaluating thunderclap headache. Curr Opin Neurol. 2021 Jun 1;34(3):356-362. doi: 10.1097/WCO.0000000000000917. PMID: 33661161.) A sentinel headache might be an alert of a stroke. (Lebedeva ER, Ushenin AV, Gurary NM, Gilev DV, Olesen J. Sentinel headache as a warning symptom of ischemic stroke. J Headache Pain. 2020 Jun 10;21(1):70. doi: 10.1186/s10194-020-01140-3. PMID: 32522256; PMCID: PMC7285795.)
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Kopel D, Peeler C, Zhu S. Headache Emergencies. Neurol Clin. 2021 May;39(2):355-372. doi: 10.1016/j.ncl.2021.01.003. PMID: 33896523
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