⚠️ Must-Not-Miss Diagnoses
Subarachnoid hemorrhage ('thunderclap'), meningitis/encephalitis, intracranial mass with herniation, venous sinus thrombosis, hypertensive emergency, carotid/vertebral artery dissection, giant cell arteritis (in elderly).
Differential Diagnosis by Key Features
| Clinical Feature | Think Of | Priority |
|---|---|---|
| Thunderclap — worst headache of life, maximal at onset | Subarachnoid hemorrhage | HIGH — LP even if CT negative |
| Fever + meningismus + photophobia/phonophobia | Meningitis | HIGH |
| New headache >50 years old, jaw claudication, scalp tenderness | Giant cell arteritis | HIGH |
| Positional (worse lying down), papilledema, morning nausea/vomiting | Raised ICP / mass | HIGH |
| Unilateral, pulsating, nausea/vomiting, photophobia, aura | Migraine | Benign |
| Bilateral, pressure/tightening, stress-related | Tension-type | Benign |
| Periorbital, unilateral, excruciating, autonomic features, clusters | Cluster headache | Benign |
Systematic Approach
Red Flags
SNOOP4 criteria
Secondary headache red flags: Systemic illness/fever, Neurologic deficits, Onset sudden (thunderclap), Older age (>50 new headache), Progressive worsening, Positional, Papilledema, Precipitated by Valsalva. Any of these warrants urgent evaluation.
Thunderclap
CT then LP
Thunderclap headache (maximal at onset, 'worst headache of life') = presumptive SAH until proven otherwise. Non-contrast CT has ~93% sensitivity in first 6 hours. LP with xanthochromia analysis is required if CT negative but clinical suspicion high.
Exam
Fundoscopy + meningismus + neuro exam
Papilledema = raised ICP. Meningismus = meningitis/SAH. Focal deficit = structural lesion. Temporal artery tenderness = giant cell arteritis. Horner's syndrome + neck pain = carotid dissection.
Primary Headache
Diagnose by criteria after excluding secondary causes
International Headache Society criteria define migraine, tension-type, and cluster. Treat empirically with appropriate agents once secondary causes excluded. Migraine: triptans + NSAIDs. Tension: NSAIDs. Cluster: O2 + sumatriptan.
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