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Assessment and investigation of thunderclap headache

BMJ 2025; 389 doi: https://doi.org/10.1136/bmj-2024-083247 (Published 15 May 2025) Cite this as: BMJ 2025;389:2024-083247
  1. Hans Rosenberg, emergency physician1,
  2. Katie Y Lin, emergency physician12,
  3. Albert Y Jin, neurologist3,
  4. Jeffrey J Perry, emergency physician14
  1. 1Department of Emergency Medicine, University of Ottawa, Ottawa, Ontario, Canada
  2. 2Department of Emergency Medicine and Department of Clinical Neurosciences, University of Calgary, Calgary, Alberta, Canada
  3. 3Department of Medicine, Division of Neurology, Queen’s University, Kingston General Hospital, Kingston, Ontario, Canada
  4. 4Ottawa Hospital Research Institute, Ottawa, Ontario, Canada
  1. Correspondence to: H Rosenberg hrosenberg{at}toh.ca

What you need to know

  • Thunderclap headache is associated with high risk aetiologies, such as subarachnoid haemorrhage and intracranial haemorrhage.

  • Delayed diagnosis is associated with worse clinical outcomes.

  • The Ottawa subarachnoid haemorrhage rule has a high sensitivity and low specificity. It can help identify patients who are at low risk for non-traumatic subarachnoid haemorrhage and reduce unnecessary investigations.

  • Early imaging (non-contrast CT (computed tomography) within 6 hours) and, if necessary, lumbar puncture, are first line diagnostic investigations.

  • CT angiography for subarachnoid haemorrhage can identify vascular causes of thunderclap headache and could be an alternative to lumbar puncture in select cases.

A 63 year old man presents to the emergency department with severe, sudden onset headache eight hours before arrival. He appears uncomfortable but is alert and oriented. His blood pressure is 165/110 mm Hg, otherwise his vital signs are normal. He has a history of depression, for which he takes escitalopram.

Undifferentiated headache is one of the most common neurological symptoms presenting to primary care and emergency departments worldwide.12 Headache represents 1-4% of all emergency department presentations and thunderclap headache accounts for about 14% of those cases, according to a multinational observational study performed across high and middle income countries.3

Thunderclap headache refers to severe headache of sudden onset. Whereas some studies define sudden onset as reaching maximum intensity immediately, within one minute or less, and lasting for five minutes or longer, studies investigating diagnoses associated with increased risk of acute morbidity and/or mortality, related to an acute headache, have tended to use a time of up to one hour until maximum intensity.4567 As such, we believe that the assessment of patients suspected of having a thunderclap headache should not be limited to those whose maximum intensity peaks within one minute, but rather up to one hour. …

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