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Thunderclap Headache - what is it?

Thunderclap headache describes an sudden severe headache which is at its worst at the very start.

It affects about 40 people per 100,000 each year. So a typical acute hospital serving 250,000 people will see 1-2 cases each week.

The classic story is a headache occurring out of the blue, or during exercise.

When asked about this pain, most people (over 85%) will say it developed over no more than 2-3 seconds, and persisted at a high intensity for at least 15 minutes.

The pain can be experienced either in the back of the head only, over the front of the head or suddenly appear over the entire head.

The pain will involve both sides of the head.

Thunderclap Headache is a not a term for describing headache that is felt on one side of the head only.

When taking a headache history, make sure you know, before you proceed to examination or tests the exact onset of the headache.

The biggest mistake in assessing this type of severe headache is not realising that you are dealing with a headache that is acute, severe and maximal at onset.

Thunderclap Headache can stroke like a thunderbolt - out of the blue and is sudden, severe, maximal at onset.

You should ask the question-

"From the start of your headache until it reached its worst - How long did it take?"

- or a poor outcome is possible.

This poor outcome is for your patient (who may sustain a preventable disability or death).

You, your defence union or employer are also in for a poor outcome - if a sudden severe headache is not properly assessed, you may miss a diagnosis of subarachnoid haemorrhage.

Failure to diagnose subarachnoid haemorrhage is still a cause of litigation and major compensation claims.

85% of subarachnoid haemorrhage is due to a weakness in a brain blood vessel called a berry aneurysm. If a first bleed is diagnosed it is possible to treat brain artery aneurysms and prevent a second bleed.

If a berry aneurysm is not diagnosed, it may bleed again. These second bleeds (re-bleeds) are more severe than the first, and are highly likely to cause major disability or death.

For that reason alone a sudden severe, maximal at onset headache requires careful assessment - you do not want to be caught out, yet you do not want to subject your patient to unnecessary investigation.

The usual reason for misdiagnosis is not being aware that at the very start, the headache was of thunderclap type.

Although the symptom is very alarming, it is often the case that diagnostic tests, including CT Brain Scan and Lumbar Puncture are normal (in 90% of cases).

However, knowledge of this topic is increasing rapidly, and there is a lot of interest in conditions such as the reversible cerebral vasoconstriction syndrome.

As methods of studying blood vessels of the brain improve e.g. MRI Angiography, our understanding of this severe headache disorder will surely increase.

Thrombosis of a venous sinus is a rare cause of thunderclap headache, as shown on this CT Brain Scan (Creative Commons License)

Causes of Thunderclap Headache

If you search the medical literature you can find many different causes or conditions associated with this sudden severe headache disorder.

This list of causes is what is called the thunderclap headache differential diagnosis:

Primary Thunderclap Headache

This means that after a typical episode, no cause was found after a CT Brain and a Lumbar Puncture Procedure. It is increasingly common to perform MRI Brain imaging, but I would recommend that a neurologist is consulted before proceeding with MRI in acute headache investigation.