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  • Age > 40 years.

  • Rapid onset and severe intensity (ie, “thunderclap” headache), trauma, onset during exertion.

  • Fever, vision changes, neck stiffness.

  • HIV infection.

  • Current or past history of hypertension.

  • Neurologic findings (mental status changes, motor or sensory deficits, loss of consciousness).


Approximately 90% of people in the United States experience a headache in their lifetime. It accounts for approximately 13 million visits each year to physicians' offices, urgent care clinics, and emergency departments in the United States. It is the fifth most common reason for emergency department visits, and second most common reason for neurologic consultation in the emergency department. Approximately 2–4% of all patients who seek medical attention in an emergency department report symptoms of nontraumatic headache. A broad range of disorders can cause headache (see Chapter 24). This section deals only with acute nontraumatic headache in adults and adolescents. The challenge in the initial evaluation of acute headache is to identify which patients are presenting with an uncommon but life-threatening condition; approximately 1% of patients seeking care in emergency department settings and considerably less in office practice settings fall into this category.

Diminution of headache in response to typical migraine therapies (such as serotonin receptor antagonists or ketorolac) does not rule out critical conditions such as subarachnoid hemorrhage or meningitis as the underlying cause. A “sentinel headache” before a subarachnoid hemorrhage is a sudden, intense, persistent headache different from previous headaches; it precedes subarachnoid hemorrhage by days or weeks and occurs in 15–60% of patients with spontaneous subarachnoid hemorrhage.

COVID-19 infection may cause acute headache, an increase in acute migraine frequency, worsening of chronic migraines, and may increase the frequency of cerebral venous thrombosis and cerebral venous sinus thrombosis.


A. Symptoms

A careful history and physical examination should aim to identify causes of acute headache that require immediate treatment. These causes can be broadly classified as (1) imminent or completed vascular events (intracranial hemorrhage, thrombosis, cavernous sinus thrombosis, vasculitis, malignant hypertension, arterial dissection, cerebral venous thrombosis, transient ischemic attack, or aneurysm; (2) infections (abscess, encephalitis, or meningitis), intracranial masses causing intracranial hypertension, preeclampsia; and (3) carbon monoxide poisoning and methemoglobinemia. Having the patient carefully describe the onset of headache can help diagnose a serious cause.

Report of a sudden-onset headache that reaches maximal and severe intensity within seconds or a few minutes is the classic description of a “thunderclap” headache; it should precipitate workup for subarachnoid hemorrhage, since the estimated prevalence of subarachnoid hemorrhage in patients with thunderclap headache is 43%. In a case series with 42 patients who had bled from an aneurysm, the headache came instantly in 50%, after 2–60 seconds in 24%, and within 1–5 minutes in 19%.

Thunderclap headache during the postpartum period precipitated by the Valsalva maneuver or recumbent positioning may indicate ...

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