Thunderclap headache

A non-haemorrhagic "thunderclap" headache (TCH) is a diagnosis of exclusion made in patients who present with severe headache but have a negative CT and LP.

• differential diagnosis with the sentinel headache observed during the development of an aneurysmal rupture is extremely important (1,2)
  • all patients with TCH should be investigated with at least a CT scan and MR angiography, since this type of headache is not a frequent benign recurrent headache disorder, and may represent a serious underlying process
  • thunderclap headache is associated with high-risk aetiologies, such as subarachnoid haemorrhage and intracranial haemorrhage (3)

TCH is defined by the ICHD-II as a severe intense headache which is of rapid onset mimicking a subarachnoid haemorrhage (SAH) from a ruptured aneurysm with maximum intensity being reached in less than a minute (1)

• the incidence in the developed world is estimated to be around 43 per 100,000 adults per year

Thunderclap headaches can be

• primary
  • diagnosed when no underlying cause is discovered
  • ICHD-II classification states that normal brain imaging and CSF are required before a diagnosis (1,2)
  • although introduced in the second version of the International Classification of Headache Disorders as a different entity, there are doubts about whether primary thunderclap headaches really exists
  • diagnosis of primary thunderclap headache should be considered only when all other causes have been demonstrably excluded (3)
• secondary
  • consider a diagnosis of subarachnoid haemorrhage in patients who present with thunderclap headache (3)
  • other possible causes include (3):
    • intracranial haemorrhage
    • acute ischaemic stroke
    • dissection: carotid, vertebral, or basilar
    • reversible cerebral vasoconstriction syndrome
    • meningitis; acute angle closure glaucoma
    • pituitary apoplexy
    • cerebral venous sinus thrombosis
    • posterior reversible encephalopathy syndrome
    • cerebrospinal fluid leak causing intracranial hypotension
    • third ventricle tumour or colloid cyst
    • cardiac cephalgia secondary to myocardial infarction
    • phaeochromocytoma

Patients with a first presentation of thunderclap headache should be referred immediately to hospital for same-day specialist assessment (1,2).

Ottawa subarachnoid haemorrhage rule has a high sensitivity and low specificity (3):

• can help identify patients who are at low risk for non-traumatic subarachnoid haemorrhage and reduce unnecessary investigations

First-line diagnostic investigations are early imaging (non-contrast CT (computed tomography) within 6 hours) and, if necessary, lumbar puncture (3):

• if a diagnosis of subarachnoid haemorrhage is established via a positive non-contrast CT head or a lumbar puncture that is considered positive or equivocal, then proceed to a CT angiogram of the brain to confirm the diagnosis (aneurysmal versus non-aneurysmal subarachnoid haemorrhage) and to guide definitive management
• note that CT angiography for subarachnoid haemorrhage can identify vascular causes of thunderclap headache and could be an alternative to lumbar puncture in select cases

Notes (1,2):

• the pathophysiology of TCH in the absence of underlying pathology is not well understood
  • primary TCH has a distinctive clinical and angiographic profile and must be distinguished from central nervous system vasculitis and SAH

References:

1. SIGN (March 2008).Diagnosis and Management of headaches in adult.
2. NICE. Headaches in over 12s: diagnosis and management. Clinical guideline CG150. Published September 2012, last updated December 2021.
3. Rosenberg H, Lin K Y, Jin A Y, Perry J J. Assessment and investigation of thunderclap headache. BMJ 2025; 389 :2024-083247.