Approach To Headache

1. THE PATHOPHYSIOLOGY

• Pain-Sensitive vs. Pain-Insensitive Intracranial Structures: The brain parenchyma itself, the majority of the overlying meninges, the ependymal lining, and the choroid plexus do not possess pain receptors. Intracranial pain arises from traction, compression, inflammation, or distention of pain-sensitive structures: the dura mater, dural venous sinuses, major intracranial and meningeal arteries, and sensory cranial nerves (CN V, IX, X, and C1–C3 nerve roots). Extracranial sources include scalp vessels, pericranial muscles, cervical nerve roots, eyes, teeth, and paranasal sinuses.
• Trigeminal System & Neurogenic Inflammation: Vascular and meningeal head pain is primarily mediated via the ophthalmic division of the trigeminal nerve (CN V1). Nociceptive discharges travel along unmyelinated C fibers (slow, burning/throbbing pain) and myelinated A-\(\delta\) fibers (sharp, localized pain) to the trigeminal nucleus caudalis and upper cervical spinal cord (C1–C2).
• Migraine Pathophysiology: The historical theory of primary vasoconstriction followed by rebound vasodilation has been refuted. Migraine is a primary neurovascular disorder driven by abnormal trigeminal and thalamic activation, accompanied by the antidromic release of vasoactive neuropeptides (substance P, calcitonin gene-related peptide [CGRP], neurokinin A) causing sterile neurogenic inflammation and perivascular sensitization. Cortical Spreading Depression (CSD)—a self-propagating wave of neuronal and glial depolarization across the cerebral cortex—drives the focal neurological symptoms of the migraine aura.
• Trigeminal Autonomic Cephalalgias (Cluster Headache): Involves central trigeminal activation coupled with central parasympathetic autonomic reflex outflow via the facial nerve and sphenopalatine ganglion, producing severe unilateral orbital pain with ipsilateral autonomic phenomena (lacrimation, rhinorrhea, nasal congestion, miosis, ptosis).
• Intracranial Pressure (ICP) Alterations & Mechanical Traction:
• Elevated ICP: Mass lesions, hydrocephalus, or cerebral edema displace brain tissue and exert mechanical traction on pain-sensitive dural structures and tentorial arteries. Pain is characteristically exacerbated by recumbency, coughing, or Valsalva maneuvers.
• Low ICP / Post-Dural Puncture Headache (PDPH): Persistent CSF leakage (following dural puncture or spontaneous dural tear) decreases CSF volume and pressure (\(<6\text{ cm H}_2\text{O}\)), stripping the brain of its natural fluid buoyancy. When upright, gravity causes the brain to descend vertically within the skull, placing direct mechanical traction on pain-sensitive sensory nerves and dural bridging veins, generating classic orthostatic headache.

2. THE CRITICAL DDx MATRIX

                    HEADACHE EMERGENCY RISK STRATIFICATION
                                      │
         ┌────────────────────────────┴────────────────────────────┐
         ▼                                                         ▼
  [ KILL IN MINUTES ]                                       [ KILL IN HOURS ]
(Immediate Catastrophic Vascular,                         (Progressive Infection, Thrombosis,
 Resuscitative & Pressure Crises)                           Vasculitis & Mass Effect)
 ── Aneurysmal Subarachnoid Hemorrhage (SAH)               ── Acute Bacterial Meningitis / Encephalitis
 ── Acute Intracerebral / Cerebellar Hemorrhage            ── Cerebral Venous Sinus Thrombosis (CVST)
 ── Cervical Artery Dissection (Carotid/Vertebral)        ── Giant Cell / Temporal Arteritis (GCA)
 ── Pituitary Apoplexy                                     ── Reversible Cerebral Vasoconstriction (RCVS)
 ── Acute Angle-Closure Glaucoma                           ── Intracranial Mass / Brain Abscess
 ── Acute Carbon Monoxide (CO) Poisoning                   ── Preeclampsia / Eclampsia

Kill in Minutes (Catastrophic Vascular, Pressure & Toxic Disasters)

• Aneurysmal Subarachnoid Hemorrhage (SAH): Rupture of an intracranial berry aneurysm; accounts for 11%–25% of all "thunderclap" headaches. Carries a 50% 30-day mortality rate. Peak risk of rebleeding occurs within the first 2 to 12 hours.
• Acute Intracerebral / Cerebellar Hemorrhage: Acute parenchymal bleeding with rapid mass effect. Cerebellar hemorrhages (10% of ICH cases) can abruptly cause brainstem compression, tonsillar herniation, acute hydrocephalus, and coma, requiring emergent neurosurgical decompression.
• Cervical Artery Dissection (Carotid or Vertebral): Intimal tear leading to arterial stenosis, occlusion, or embolic stroke. Presents as thunderclap or unilateral neck/head pain, accompanied by a partial Horner’s syndrome (ptosis and miosis without anhidrosis) in 25% of cases or cranial nerve palsies.
• Pituitary Apoplexy: Acute hemorrhagic infarction or necrosis of a pituitary adenoma. Causes sudden thunderclap headache, severe nausea, bitemporal hemianopsia, ophthalmoplegia, and acute fulminant adrenal crisis.
• Acute Angle-Closure Glaucoma: Ocular emergency caused by pupillary block; intraocular pressure (IOP) spikes \(>30\text{ mmHg}\) (normal \(\le 21\text{ mmHg}\)). Presents with severe headache, eye pain, mid-dilated sluggish pupil, clouding of vision, and visual halos; causes permanent optic nerve blindness if not rapidly lowered.
• Carbon Monoxide (CO) Toxicity: Inhalation of odorless CO gas causing carboxyhemoglobinemia (\(COHb\)) and profound cellular hypoxia. Classically presents with headache affecting multiple household members or pets; severe exposure leads to coma, seizures, myocardial ischemia, and death.

Kill in Hours (Progressive Infection, Thrombosis, Vasculitis & Raised ICP)

• Acute Bacterial Meningitis / Encephalitis: Fulminant infection of the subarachnoid space. Triad of fever, neck stiffness (meningismus), and altered mental status (absence of all 3 makes meningitis unlikely); leads to cerebral edema, raised ICP, and septic shock.
• Cerebral Venous Sinus Thrombosis (CVST): Occlusion of dural venous sinuses (sagittal or transverse). Occurs in hypercoagulable patients (pregnancy, puerperium, oral contraceptives, inherited thrombophilias). Presents with progressive or thunderclap headache, papilledema, seizures (40%), and venous hemorrhagic infarctions.
• Giant Cell / Temporal Arteritis (GCA): Systemic granulomatous vasculitis affecting medium and large arteries in adults \(>50\) years old. Presents with new unilateral headache, temporal artery tenderness, jaw claudication, ESR \(>50\text{ mm/h}\), or elevated CRP; carries a catastrophic risk of permanent, irreversible anterior ischemic optic neuropathy / blindness if corticosteroid therapy is delayed.
• Reversible Cerebral Vasoconstriction Syndrome (RCVS): Reversible segmental cerebral arterial constriction. Characterized by recurrent thunderclap headaches over days to weeks, with risk of ischemic or hemorrhagic stroke.
• Intracranial Mass / Brain Abscess: Space-occupying lesions causing CSF obstruction and intracranial hypertension. Features include morning/nocturnal headache awakening the patient, pain exacerbated by Valsalva, papilledema, or progressive focal neurologic deficits.
• Preeclampsia / Eclampsia: Occurs at \(>20\) weeks gestation or up to 6 weeks postpartum. Characterized by BP \(\ge 140/90\text{ mmHg}\) and end-organ dysfunction. New-onset headache resistant to acetaminophen is a severe feature heraldic of eclamptic seizures, PRES, or intracranial bleeding.

3. THE DIAGNOSTIC ENGINE

                     EMERGENCY HEADACHE WORKUP ALGORITHM
                                      │
            [ Doorway Assessment: ABCs, GCS, POC Glucose, Vitals ]
                                      │
         ┌────────────────────────────┴────────────────────────────┐
         ▼                                                         ▼
  [ High-Risk Red Flags Present ]                          [ Low-Risk / Primary ]
  - SNOOP2: Sudden thunderclap,                            - Known primary headache
    New >50y, Focal neuro deficit,                           concordant with prior pattern
    Fever, Immunocompromised, Cancer,                      - Normal physical & neuro exam
    Pregnancy, Anticoagulant use                           - Benign presentation
         │                                                         │
         ▼                                                         ▼
  [ Emergent Non-Contrast Head CT ]                        [ Empiric Symptom Control ]
         │                                                 (Metoclopramide / Ketorolac /
         ├─────────────────────────────────┐                Triptans; No Opioids)
         ▼                                 ▼
   [ CT Positive ]                   [ CT Negative ]
 (Bleed, Mass, Hydrocephalus)              │
         │                                 ├──────────────────────────────────┐
         ▼                                 ▼                                  ▼
   [ Specific Therapy /             [ Pain Onset <6 Hours ]            [ Pain Onset >6 Hours ]
     Neurosurg Consult ]           - NCCT sensitivity ~100%           - CT sensitivity drops
                                   - SAH excluded (Ottawa Rule)       - MANDATORY Secondary Test:
                                   - Consider discharge if benign       * Lumbar Puncture (CSF RBC/Xanthochromia)
                                                                        * OR CT Angiography (CTA)

Step 1: High-Risk Red Flag Screening (Modified SNOOP2 Criteria)

Prioritize identifying secondary "can't-miss" etiologies by screening for red flags:

• S: Systemic symptoms (fever, night sweats, weight loss) or Secondary risk factors (malignancy, HIV/immunocompromise, pregnancy/postpartum, anticoagulation/antiplatelet use).
• N: Neurologic deficits or altered mental status (confusion, lethargy, seizures, ataxia, cranial nerve palsies).
• O: Onset sudden or abrupt ("thunderclap" reaching maximum intensity within 1 minute).
• O: Older age (\(>50\) years with a new or changing headache—carries a 4- to 6-fold higher rate of dangerous pathology).
• P: Pattern change or Progression (subacute worsening over weeks, awakening from sleep, aggravated by Valsalva, coughing, or postural changes).
• P: Papilledema / Pulsatile tinnitus / Post-traumatic / Postcoital or Exertional onset.

Step 2: Clinical Decision Aid — Ottawa Subarachnoid Hemorrhage Rule

Applies to alert patients \(\ge 15\) years old presenting with a new, severe atraumatic headache peaking within 1 hour.

• Exclusions: New focal neurologic deficits, prior brain aneurysm, prior SAH, known brain tumor, or chronic recurrent headaches.
• Decision Criteria: If ANY of the following 6 features are present, the patient cannot be ruled out for SAH and requires neuroimaging:

    1.  Age \\(\ge 40\\) years
    2.  Neck pain or stiffness
    3.  Witnessed loss of consciousness
    4.  Onset during physical exertion
    5.  Thunderclap headache (instant peak pain)
    6.  Limited neck flexion on physical examination

• Utility: The Ottawa SAH rule possesses a validated 100% sensitivity for ruling out SAH.

Step 3: Neuroimaging Strategy (Emergent Non-Contrast Head CT)

• Emergent Head CT Indications: Thunderclap headache, new focal neurologic deficit, altered mental status, papilledema, HIV-positive with new headache, age \(>50\) with new headache, or head trauma.
• The 6-Hour CT Window Rule: Performing a non-contrast head CT on a modern 3rd-generation scanner within 6 hours of headache onset carries a sensitivity approaching 100% (99.4%–100%) and a negative predictive value of 99.4% for aneurysmal SAH.
• Beyond 6 Hours: CT sensitivity drops to 90%–93% at 24 hours and 50% at 1 week due to blood resorption. A normal head CT performed \(>6\) hours after onset CANNOT rule out SAH; secondary testing is mandatory.

Step 4: Secondary Testing — Lumbar Puncture (LP) vs. CT Angiography (CTA)

• Lumbar Puncture Indications:

    1.  Head CT is negative but performed \\(>6\\) hours from headache onset in a patient with suspected SAH (evaluating for CSF xanthochromia and persistent RBCs in tube 4).
    2.  Suspected central nervous system infection (meningitis, encephalitis).
    3.  Suspected Idiopathic Intracranial Hypertension (measuring opening pressure \\(>250\text{ mm H}_2\text{O}\\)).

• Indications for CT Before LP (IDSA / ED Guidelines): Obtain a head CT prior to LP to exclude mass effect or midline shift (preventing brain herniation) if the patient has:
• Immunocompromised state (e.g., HIV, immunosuppressants)
• Known history of CNS disease (mass, stroke)
• New-onset seizure
• Altered level of consciousness / GCS \(<15\)
• Focal neurological deficit
• Papilledema on examination
• CT Angiography (CTA) Alternative: The 2019 ACEP clinical policy endorses CT Angiography (CTA) of the head and neck as a valid alternative to LP (Level C recommendation) when clinical concern for aneurysmal SAH persists despite a negative non-contrast head CT. CTA/MRA is also the primary diagnostic test for cervical artery dissection and RCVS, whereas MRV/CTV is required for CVST.

4. EMPIRIC MANAGEMENT

Emergency Stabilization & Specific Conditions

• Airway & Raised ICP Resuscitation:
• Elevate head of bed 30 degrees in the midline to facilitate venous drainage.
• Target normocapnia (\(PaCO_2\) 35–40 mmHg) and normoxia (\(SpO_2 \ge 94%\)); avoid routine hyperventilation unless active transtentorial herniation is occurring.
• Administer hyperosmolar therapy: Mannitol 0.5 to 1.0 g/kg IV or Hypertonic Saline.
• For tumor-associated vasogenic cerebral edema, give Dexamethasone 10 mg IV loading dose, followed by 4 mg IV every 6 hours.
• Aneurysmal Subarachnoid Hemorrhage:
• Blood Pressure Control: Maintain SBP \(<160\text{ mmHg}\) (target 120–160 mmHg) using titratable IV agents such as Nicardipine infusion (5–15 mg/h) or Labetalol IV (10–20 mg bolus). Avoid nitroglycerin and nitroprusside, as they induce cerebral vasodilation and increase ICP.
• Vasospasm Prevention: Initiate oral Nimodipine 60 mg PO/NG every 4 hours.
• Empiric Bacterial Meningitis: Never delay antibiotics for imaging or LP! Immediately administer Ceftriaxone 2 g IV + Vancomycin 15–20 mg/kg IV (+ Ampicillin 2 g IV if age \(>50\) or immunocompromised) along with Dexamethasone 10 mg IV (administered prior to or with the first dose of antibiotics).
• Giant Cell Arteritis: Immediately initiate high-dose Prednisone 60 mg PO daily (or IV Methylprednisolone 1 g daily if visual loss is present) prior to temporal artery biopsy to preserve vision.
• Preeclampsia with Severe Features: Administer Magnesium Sulfate 4–6 g IV loading dose (for eclamptic seizure prophylaxis) + IV Labetalol or Hydralazine / oral Nifedipine for severe BP control.

Primary Headache Abortive Therapies (Migraine & Tension)

                  FIRST-LINE ED MIGRAINE COCKTAIL
                                  │
         ┌────────────────────────┼────────────────────────┐
         ▼                        ▼                        ▼
  [ Antidopaminergic ]     [ Parenteral NSAID ]     [ Extrapyramidal Cover ]
 - Metoclopramide 10mg IV  - Ketorolac 15-30mg IV   - Diphenhydramine 25-50mg IV
   OR Prochlorperazine       (Avoid if bleed/renal/   (Prevents akathisia &
   10mg IV                   pregnancy)               dystonic reactions)

• First-Line Antidopaminergic Antiemetics:
• Metoclopramide 10 mg IV OR Prochlorperazine 10 mg IV (or Droperidol 1.25–2.5 mg IM / Haloperidol 2.5–5 mg IV).
• Akathisia Prevention: Co-administer Diphenhydramine 25 to 50 mg IV to prevent dopamine-antagonist-induced extrapyramidal dystonic reactions and akathisia.
• Pregnancy: Metoclopramide 10 mg IV is the first-line drug of choice in pregnancy.
• Parenteral NSAIDs: Ketorolac 15 to 30 mg IV/IM. Contraindicated in intracranial hemorrhage, active GI bleeding, severe renal impairment, or pregnancy.
• Triptans: Sumatriptan 6 mg Subcutaneous. Contraindicated in ischemic heart disease, uncontrolled hypertension, peripheral vascular disease, cerebrovascular disease, or pregnancy.
• Recurrence Prevention: Dexamethasone 10 mg IV/IM administered in the ED significantly reduces migraine recurrence rates within 72 hours of discharge.
• Cluster Headache: Administer 100% High-Flow Oxygen at 12–15 L/min via non-rebreather mask for 15–20 minutes PLUS Sumatriptan 6 mg SC.
• Opioid Rule: Opioids are strictly NOT recommended as first-line therapy for primary headaches in the ED. Opioids induce central hyperalgesia, cause medication overuse headaches, and lead to high ED recidivism rates.

5. THE DISPOSITION TRAPS

• The "Pain Relief Proves Benign Etiology" Trap:
• Cognitive Error: Assuming that because a patient's severe headache resolves following ED administration of a "migraine cocktail," antiemetics, or analgesics, dangerous secondary pathology has been ruled out.
• Clinical Reality: Symptomatic relief of pain occurs in up to 50% of patients with subarachnoid hemorrhage, cervical dissection, or meningitis following simple analgesics; pain response cannot be used to exclude life-threatening disease.
• The "\(>6\)-Hour CT Rule" Diagnostic Trap:
• Cognitive Error: Relying solely on a negative non-contrast head CT to rule out SAH when the imaging was performed more than 6 hours after headache onset.
• Clinical Reality: While CT sensitivity within 6 hours approaches 100%, sensitivity degrades rapidly to 90%–93% at 24 hours and 50% at 1 week. A normal head CT \(>6\) hours from onset requires a secondary lumbar puncture or CT angiography to definitively exclude SAH.
• The "Standard Pulse Oximetry" Carbon Monoxide Trap:
• Cognitive Error: Relying on a normal pulse oximetry (\(SpO_2\)) reading to exclude carbon monoxide poisoning in a patient presenting with headache.
• Clinical Reality: Standard two-wavelength pulse oximeters cannot distinguish carboxyhemoglobin from oxyhemoglobin and will display a falsely normal 98%–100% saturation. Direct blood co-oximetry is mandatory.
• The "Afebrile Means No Meningitis" Trap:
• Cognitive Error: Ruling out bacterial meningitis or brain abscess because the patient presents without a fever or classic nuchal rigidity.
• Clinical Reality: Elderly, immunocompromised (HIV CD4 \(<200\)), and partially antibiotic-treated patients frequently lack fever or meningismus despite fulminant CNS infection.
• The "Normal Neurologic Exam in SAH" Trap:
• Cognitive Error: Assuming an alert patient with a completely normal neurological examination cannot have an aneurysmal subarachnoid hemorrhage.
• Clinical Reality: Approximately 50% of patients with aneurysmal SAH present with a completely normal neurological exam and normal mental status (Hunt and Hess Grade 1).
• The "Medication Overuse Recidivism" Discharge Trap:
• Cognitive Error: Discharging primary headache patients with outpatient prescriptions for opioids or combination analgesics.
• Clinical Reality: Frequent use (\(>10\text{ days/month}\)) of opioids, triptans, or ergots triggers severe rebound medication overuse headaches, creating a cycle of intractable pain and frequent ED readmissions. Discharge patients with a non-opioid rescue plan (e.g., naproxen 500 mg) and dexamethasone.