I have recently finished a research project which aimed to establish an effective and acceptable plan for the care of patients who go to hospital Emergency Departments with a sudden onset severe headache. The research team included researchers from the Centre for Reviews and Dissemination, doctors in emergency medicine, acute medicine and neurology at Leeds Teaching Hospitals NHS Trust, and a patient collaborator with experience of presenting to the Emergency Department with a sudden onset severe headache. An advisory group including additional patients and doctors was also involved throughout the project.

Sudden onset severe headache

Approximately 2% of all patients who attend an Emergency Department do so with a history of significant headache. A small proportion of these patients will provide a history that it came on suddenly. Sudden onset severe headaches can be diagnosed as a migraine or other type of headache. However, when severe headaches come on instantly, often described as feeling like a ‘thunderclap’, they can be a sign of a more serious medical condition such as subarachnoid haemorrhage (SAH).

SAH occurs when a weakened blood vessel supplying the brain suddenly bursts. This can lead to disability or death if not diagnosed and treated quickly, but diagnosis can be difficult in people who don’t show signs other than headache. Very few people who go to hospital with headache are diagnosed with SAH and many SAH patients have other symptoms in addition to headache.

Patients who go to an Emergency Department with a sudden onset severe headache (where SAH may be suspected) are given a brain scan. This is often followed by a lumbar puncture (where a sample of fluid is taken from the spine) if the brain scan is normal, to make sure a SAH hasn’t been missed.

What we looked at

We reviewed all previous research looking at clinical decision rules and diagnostic tests for assessing patients with a sudden onset severe headache.

What we found

We found 37 studies on the accuracy of clinical decision rules and diagnostic tests for ruling out SAH in people who go to hospital with a sudden onset severe headache. Our results showed:

• The Ottawa SAH clinical decision rule (Perry et al., 2013) was not very good at ruling out SAH, and using it could result in around 75% of headache patients being tested unnecessarily. There were no studies of other clinical decision rules for SAH. Clinical advisors indicated that a variety of different clinical decision rules are used in the NHS for deciding which patients require diagnostic tests for SAH.
• Brain computed tomography (CT) scans done within six hours of headache onset may be accurate enough to find all cases of SAH without the need for more testing. When assessed by radiologists who routinely read brain images, CT within six hours was over 99% accurate. However, accuracy drops considerably over time, meaning that it may be necessary to have more tests (usually lumbar puncture) if the brain scan is not done soon after headache onset.
• Lumbar puncture after CT finds any missed cases of SAH (as well as other serious conditions, such as stroke, cancer and meningitis), but 5% of results were false positives (leading to further tests), and 5-10% of patients who had a lumbar puncture returned to hospital with side effects.

The decision to do more tests to rule out SAH after a negative CT scan result should be shared between the doctor and the patient, after a discussion about the potential risks and benefits of the tests.

What does this mean for patients with migraine and other types of primary headache?

Our research findings should mean that fewer patients who go to hospital with primary headaches are given a lumbar puncture to rule out SAH after having a negative CT scan, particularly if the scan is done soon after the headache started.

If you’d like to know more about this research, the full report for this research project can be found on the Centre for Reviews and Dissemination website.