Thunderclap headache: symptoms, causes and why it needs emergency help

Most headaches build up gradually, ease with rest or simple painkillers and are not a sign of anything serious. The NHS says most headaches go away on their own. A thunderclap headache is different because of how fast it arrives. NICE describes it as a sudden severe headache, typically peaking in intensity within 1 to 5 minutes.

It is a symptom rather than a diagnosis. The doctors' job is to find out what is causing it. The NHS names thunderclap headache as the main symptom of a subarachnoid haemorrhage, a rare type of stroke that causes bleeding on the brain.

The NHS says to call 999 if you or someone you are with gets a sudden headache that is extremely painful and does not go away, or has face weakness, weakness or numbness in one arm or down one side of the body, speech problems such as slurring or confusion, or blurred vision or loss of sight in one or both eyes.

The NHS headache page gives the same instruction and adds other reasons to call 999 or go to A&E with a headache: a seizure, difficulty speaking, balance or walking, drowsiness or confusion, a rash that does not fade when a glass is rolled over it, or a very high temperature with a stiff neck or discomfort in bright lights.

The NHS says not to drive yourself to A&E. Ask someone else to drive you or call 999 for an ambulance, and bring any medicines you take. Do not wait to see whether it settles. NICE says that people seen outside hospital with a suspected subarachnoid haemorrhage should be referred to an emergency department immediately.

The defining feature is the speed: pain that starts suddenly and is extremely severe. The NHS lists the other symptoms that can come with a subarachnoid haemorrhage, and says a person may not have all of them.

It adds that a subarachnoid haemorrhage can happen at any time, but it may be more likely when you are coughing, going to the toilet, lifting something heavy or having sex. That does not mean the activity is dangerous, only that these moments have been linked with it.

• Neck pain or a stiff neck.

• Feeling or being sick.

• Being very sensitive to light.

• A seizure (fit) or shaking uncontrollably.

• Fainting, feeling sleepy or drowsy, or being confused.

• Drooping on one side of the face, slurred speech or weakness on one side of the body.

The cause the NHS focuses on is subarachnoid haemorrhage, which most commonly affects people who have a brain aneurysm, a bulge in a blood vessel in the brain, that bursts. Other causes it lists are a severe head injury and an arteriovenous malformation, a problem with the way blood vessels in the brain have formed.

NICE is clear that not every thunderclap headache is a bleed. It says thunderclap headache is associated with other conditions or causes such as migraine, cough, sex or exertion, and that most people with a thunderclap headache do not have a subarachnoid haemorrhage. It also stresses that this should not put anyone off investigation when a bleed is suspected, because people with a subarachnoid haemorrhage can present with non-specific symptoms and are at greater risk of the diagnosis being missed.

The NHS brain aneurysm page lists things that increase the chance of an aneurysm: smoking, high blood pressure, having a close relative who has had one, injury to a blood vessel in the brain, taking drugs such as cocaine, and certain genetic conditions such as autosomal dominant polycystic kidney disease or Ehlers-Danlos syndrome. It says most brain aneurysms do not cause problems.

NICE says that doctors should take a careful history to establish how fast the headache started and how quickly it reached its peak, and have a high index of suspicion for subarachnoid haemorrhage. A senior clinician reviews the person and, if the picture suggests a bleed, an urgent non-contrast CT head scan is arranged.

The scan is diagnostic if it shows blood in the space around the brain. NICE notes that CT is most accurate within 6 hours of symptom onset. If a scan done after 6 hours shows no bleed, a lumbar puncture, which samples the fluid around the spine, can be considered, and NICE says to wait at least 12 hours after the headache began before doing it.

If a bleed is found, NICE says a CT angiogram is offered without delay to look for the cause, usually an aneurysm. If no bleed is found, doctors think about other explanations for the headache.

Treatment depends on the cause. If it is a subarachnoid haemorrhage, the NHS says the main treatment is surgery to stop the bleeding, by neurosurgical clipping (a tiny metal clip seals the burst blood vessel) or endovascular coiling (tiny metal coils are passed through a thin tube from an artery in the groin or leg to block the aneurysm).

The NHS says there may also be treatment before and after surgery to help symptoms and lower the risk of rebleeding, such as medicines for pain, to lower blood pressure, to prevent seizures, to stop sickness, to soften poo and to make sure blood flows properly. If the headache turns out to have another cause, treatment follows that cause.

After a subarachnoid haemorrhage the NHS says it can take months or years to get better. Most people improve with treatment and some recover fully, but it is a very serious condition that can lead to mental and physical disability. Recovery depends on where the bleeding happened and how much damage it caused.

The NHS lists possible effects including seizures, heart, lung or liver problems, memory, concentration and communication difficulties, depression and mood changes, fatigue and headaches. Rehabilitation may include physiotherapy, speech and language therapy, cognitive behavioural therapy and cognitive exercises, and you will have regular follow-up. The NHS points to the Stroke Association for support.

Not every worrying headache is a thunderclap. The NHS advises asking for an urgent GP appointment or getting help from NHS 111 if you or a child have a headache with vision or eye problems, a headache triggered or made worse by coughing, sneezing, bending down or exercising, a headache with being sick, or a headache with jaw pain when eating or a sore or tender scalp.

For a brain aneurysm that has not burst, the NHS says to ask for an urgent appointment if you keep getting headaches, they do not go away or are getting worse, or you have pain above or around an eye. See a GP if you have tried treating a headache yourself and it is not getting better or you get headaches regularly.