Differential diagnosis of unusual headache of sudden onset

1. Big picture

An unusual headache of sudden onset is one of the most important neurological emergency presentations. The examiner wants you to think first of secondary dangerous headache, especially vascular causes.

The key exam sentence:

A sudden, severe, unusual headache — especially thunderclap headache — is subarachnoid hemorrhage until proven otherwise.

But the differential diagnosis is wider. Sudden-onset unusual headache may be caused by:

• Subarachnoid hemorrhage

• Intracerebral hemorrhage

• Cervical artery dissection

• Cerebral venous sinus thrombosis

• Reversible cerebral vasoconstriction syndrome

• Pituitary apoplexy

• Hypertensive crisis / posterior reversible encephalopathy syndrome

• Meningitis/encephalitis

• Acute glaucoma

• Brain tumor or posterior fossa lesion presenting with raised intracranial pressure

• Primary cough/exertional/sexual headache only after dangerous causes are excluded

The most important principle:

Do not diagnose migraine, tension headache, or “stress headache” in a first-ever sudden severe headache until secondary causes have been excluded.

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