Thunderclap headache

Thunderclap headache is severe headache reaching maximum intensity within one minute, with pain lasting at least 5 minutes. It is an emergency until subarachnoid haemorrhage and the other vascular causes are excluded.

Clinical relevance. Subarachnoid haemorrhage accounts for a minority of cases, but it is the cause that cannot be missed because early rebleeding carries high mortality. Several other causes of thunderclap onset are equally time critical.

Mechanisms. Sudden arterial rupture, abrupt vasoconstriction, vessel wall dissection, acute venous outflow obstruction, abrupt pressure change in the ventricular system or sella, and acute hypertension.

Classification. Secondary thunderclap headache (vascular, structural, infective, pressure related, toxic) and primary thunderclap headache. Primary thunderclap headache is a diagnosis of exclusion after full vascular imaging.

Temporal patterns. A single abrupt attack, a preceding sentinel headache days to weeks earlier, and recurrent thunderclap attacks over days to weeks (a feature of reversible cerebral vasoconstriction syndrome).

Key distinction. Time to peak is the discriminating feature: pain building over minutes to hours is a different presentation with a lower yield of dangerous causes.

History. Record the exact time of onset because CT sensitivity depends on hours since onset. Record activity at onset (exertion, sexual activity, straining, emotion, neck manipulation), location and radiation of pain, neck pain, vomiting, collapse or transient loss of consciousness, seizure, visual symptoms, and any earlier sentinel headache.

Risk factors and drug history. Hypertension, smoking, family history of subarachnoid haemorrhage, polycystic kidney disease, connective tissue disease (Marfan, Ehlers Danlos), pregnancy and the postpartum period (reversible vasoconstriction, venous thrombosis, pre-eclampsia), recent neck trauma, migraine, anticoagulants and antiplatelets. Vasoactive drugs: selective serotonin reuptake inhibitors, triptans, ergots, pseudoephedrine, cannabis, cocaine, amphetamines.

Examination. Glasgow Coma Scale, blood pressure in both arms, temperature, pulse. Neck stiffness (meningism may take 3 to 12 hours to develop and may be absent). Fundi for papilloedema and subhyaloid haemorrhage. Third nerve palsy with pupil involvement (posterior communicating artery aneurysm), Horner syndrome (carotid dissection), focal deficit, visual fields, and ECG for neurogenic changes.

Ottawa subarachnoid haemorrhage rule (alert adults over 15 years with new severe non traumatic headache reaching maximum intensity within one hour): investigate if any of the following is present: age 40 or over, neck pain or stiffness, witnessed loss of consciousness, onset during exertion, thunderclap onset (instantly peaking), or limited neck flexion on examination. The rule is highly sensitive and not specific. Do not apply it to patients with new neurological deficit, prior aneurysm, subarachnoid haemorrhage, brain tumour or recurrent headache.

Red flags

• Any reduced consciousness, seizure or focal deficit
• Meningism, fever, papilloedema, or subhyaloid haemorrhage
• Third nerve palsy
• Onset on exertion, with neck pain, or with vomiting
• Age 40 or over
• Anticoagulation or known coagulopathy
• Pregnancy or postpartum

Haemorrhagic

• Aneurysmal subarachnoid haemorrhage
• Perimesencephalic non aneurysmal subarachnoid haemorrhage
• Arteriovenous malformation bleed
• Intracerebral haemorrhage (cerebellar, lobar)
• Retroclival haematoma

Vascular, non haemorrhagic

• Reversible cerebral vasoconstriction syndrome
• Cervical or intracranial artery dissection
• Cerebral venous sinus thrombosis
• Ischaemic stroke, especially cerebellar
• Pituitary apoplexy
• Unruptured expanding aneurysm
• Hypertensive emergency and posterior reversible encephalopathy syndrome
• Pre-eclampsia and eclampsia
• Phaeochromocytoma

Structural and pressure

• Colloid cyst of the third ventricle
• Acute obstructive hydrocephalus
• Spontaneous intracranial hypotension

Infective and inflammatory

• Meningitis, encephalitis
• Acute sphenoid sinusitis

Toxic and other

• Carbon monoxide poisoning
• Acute angle closure glaucoma
• Primary cough, exertional and sexual headache
• Primary thunderclap headache

Step 1. Stabilise and examine. Obtain capillary glucose, ECG, blood pressure and, in women of reproductive age, a pregnancy test.

Step 2. Non-contrast CT head immediately. On a modern scanner within 6 hours of onset, read by a qualified radiologist, sensitivity for subarachnoid haemorrhage is close to 100 percent. Sensitivity falls progressively with each day and is poor after a week. CT also identifies intracerebral haemorrhage, hydrocephalus, mass lesions and some pituitary haemorrhage.

Step 3. If CT is normal.

• Within 6 hours of onset, in an alert patient with a technically adequate scan reported by an experienced radiologist, further testing for subarachnoid haemorrhage is usually unnecessary (evidence supports this; local scanner quality and reporting access should be considered).
• Over 6 hours from onset: lumbar puncture at least 12 hours after onset, with opening pressure, cell counts in the first and last tubes, and spectrophotometry for xanthochromia. A falling red cell count between tubes favours a traumatic tap. Alternatively, CT angiography, although this detects incidental unruptured aneurysms in about 2 to 3 percent of adults and may lead to unnecessary intervention.

Step 4. Vascular imaging. CT or MR angiography of head and neck for dissection, reversible vasoconstriction (the angiogram may be normal in the first week) and aneurysm. MRI with venography for venous sinus thrombosis. MRI with FLAIR and contrast for pituitary apoplexy, posterior reversible encephalopathy syndrome and intracranial hypotension.

Step 5. Blood tests. Full blood count, urea, creatinine, electrolytes, glucose, clotting, group and save, troponin (neurogenic cardiac injury), carboxyhaemoglobin if exposure is possible, and urine for protein in pregnancy.

Limitations. A normal CT does not exclude subarachnoid haemorrhage after 6 hours. A normal early vascular angiogram does not exclude reversible vasoconstriction. Xanthochromia is unreliable before 12 hours.

Immediate care. Airway, breathing and circulation; GCS monitoring; IV access; nil by mouth until the diagnosis is clear; head of bed at 30 degrees; avoid hypotension and hypoxia.

Symptomatic treatment. Paracetamol 1 g IV or orally every 6 hours (maximum 4 g in 24 hours). Morphine 2.5 to 5 mg IV titrated every 5 to 10 minutes if needed, with monitoring of respiratory rate and sedation. Ondansetron 4 mg IV, repeated after 8 hours if needed (maximum 16 mg in a single dose; QT monitoring). Avoid NSAIDs and aspirin until haemorrhage is excluded.

Confirmed subarachnoid haemorrhage

• Urgent neurosurgical referral; aneurysm securing (coiling or clipping) usually within 24 hours.
• Blood pressure: avoid hypotension; systolic target under 160 mmHg before the aneurysm is secured, directed by the specialist team.
• Nimodipine 60 mg orally or by nasogastric tube every 4 hours for 21 days, started within 96 hours of the haemorrhage. If blood pressure falls, 30 mg every 2 hours. In cirrhosis 30 mg every 4 hours. Never inject the contents of a capsule intravenously.
• Reverse anticoagulation: warfarin, vitamin K 5 to 10 mg IV with prothrombin complex concentrate (25 to 50 IU/kg adjusted to INR and product label); dabigatran, idarucizumab 5 g IV.
• Monitor sodium daily (hyponatraemia and cerebral salt wasting), neurological state, and for hydrocephalus and delayed cerebral ischaemia. Seizure prophylaxis is not routine.

Other confirmed causes

• Cerebral venous sinus thrombosis: enoxaparin 1 mg/kg subcutaneously every 12 hours (adjust when creatinine clearance is under 30 mL/min), even with haemorrhagic infarction, then oral anticoagulation.
• Reversible cerebral vasoconstriction syndrome: stop vasoactive drugs, control blood pressure, nimodipine 60 mg orally every 4 hours (evidence is limited), and avoid corticosteroids, which may worsen outcomes.
• Pituitary apoplexy: hydrocortisone 100 mg IV then 50 mg IV every 6 hours, with neurosurgical and endocrine referral.
• Cervical artery dissection: antithrombotic therapy directed by the stroke team.
• Meningitis and encephalitis: ceftriaxone 2 g IV every 12 hours with dexamethasone 10 mg IV every 6 hours for 4 days; aciclovir 10 mg/kg IV every 8 hours if encephalitis is suspected.

Monitoring. Neurological observations hourly initially, blood pressure continuously, sodium daily.

Referral and escalation. Neurosurgery for subarachnoid haemorrhage, hydrocephalus and structural lesions; stroke or neurology for dissection, venous thrombosis and vasoconstriction; obstetrics for pregnancy related causes. Urgency is immediate.

Admission and discharge. Admit all confirmed causes. Discharge only after a normal CT within 6 hours of onset in an alert, neurologically intact patient with reliable reporting, or after normal CT plus lumbar puncture or angiography when later. Patients with a normal work up and a primary thunderclap headache still need outpatient neurology review.

Safety netting. Return immediately for recurrent sudden headache, vomiting, drowsiness, weakness, speech or visual change, or seizure.