Stroke

What it is

A stroke can affect movement, speech, vision, thinking and emotions, and may be life-threatening⁹.

There are two main types. In an ischaemic stroke, a blood clot or narrowed artery blocks blood flow; this accounted for about 65% of new strokes worldwide in 2021¹. In a haemorrhagic stroke, a blood vessel bursts, either within the brain (intracerebral haemorrhage, about 29%) or into the space around it (subarachnoid haemorrhage, about 6%)¹.

A transient ischaemic attack (TIA), sometimes called a mini-stroke, causes stroke symptoms that resolve quickly but is a warning sign that needs urgent assessment^8,9. In 2021 there were about 94 million people living after a stroke, and the global burden has grown since 1990¹.

SideFrontAbove

Approximate area supplied by the middle cerebral artery, which serves much of the outer surface of the frontal, parietal and temporal lobes and, through small branches, deep structures. A blocked artery leaves a core of dying tissue surrounded by a penumbra that can still be saved if blood flow returns in time².

Signs and symptoms

Stroke symptoms start suddenly. The FAST test helps people recognise the most common signs: Face, Arms, Speech, Time to call emergency services⁹.

• Face: one side of the face may droop and it may be hard to smile⁹.
• Arms: weakness or numbness in one arm, so both cannot be lifted and held up⁹.
• Speech: slurred or confused speech, or difficulty finding words⁹.
• Weakness or numbness down one side of the body⁹.
• Blurred vision or loss of sight in one or both eyes⁹.
• Dizziness, loss of balance, confusion, a sudden severe headache, or nausea and vomiting⁹.

Causes and risk factors

Ischaemic strokes are usually caused by clots that form on fatty deposits in arteries (atherosclerosis), travel from the heart, or block small vessels deep in the brain². High blood pressure is especially strongly associated with intracerebral haemorrhage and is its most common cause^3,16. An international study in 32 countries found that ten potentially modifiable risk factors together accounted for about 90% of the population risk of stroke, consistently across regions, sexes and ages³.

• High blood pressure, the most important single factor, associated with nearly half of stroke risk in that study³.
• Physical inactivity, unhealthy diet, abdominal obesity and an unfavourable blood fat profile³.
• Smoking, high alcohol intake and psychosocial stress³.
• Heart conditions, including atrial fibrillation, an irregular heart rhythm that allows clots to form in the heart, and diabetes^2,3.
• Age over 50, a previous stroke or TIA, sickle cell disease, and Black or South Asian background¹⁰.
• Rising burdens from high body mass index, high blood sugar and air pollution have been reported globally¹.

Genetics

Most strokes result from the combined effects of many common genetic variants together with lifestyle and vascular risk factors. A cross-ancestry genome-wide association study of more than 110,000 people who had had a stroke identified 89 risk regions and highlighted possible drug targets¹².

Genetic risk scores built from these findings can help predict ischaemic stroke, but they are not yet used routinely in clinical care¹².

A small proportion of strokes have a single-gene cause. The most common heritable cause of stroke in adults is CADASIL, caused by variants in the NOTCH3 gene; it leads to damage of small arteries, early strokes, migraine with aura and vascular dementia¹³.

What happens in the brain

The brain depends on a continuous supply of oxygen and glucose. When an artery is blocked, a core of tissue dies rapidly, while a surrounding region, the penumbra, is starved of blood but can still be saved if blood flow is restored in time².

In a typical large ischaemic stroke, an estimated 1.9 million neurons are lost each minute without treatment, which is why the phrase “time is brain” is used⁴.

In haemorrhagic stroke, blood leaking into or around the brain damages tissue directly and raises pressure inside the skull¹⁶. The type of stroke must be identified before treatment because clot-dissolving medicines would worsen bleeding⁸.

How it is diagnosed

In India, the ICMR Standard Treatment Workflow advises rapid transfer to the nearest hospital with a CT scanner or to a stroke centre able to give thrombolysis¹⁷. Stroke is diagnosed from the sudden onset of symptoms and an urgent clinical assessment, often using validated recognition tools in the emergency department⁸. Low blood sugar, which can mimic stroke, must be excluded⁸.

• Immediate brain imaging, usually a CT (computed tomography) scan, distinguishes bleeding from blockage and identifies people who may benefit from clot-removing treatment⁸.
• CT or MR angiography, which shows the blood vessels, confirms large artery blockages suitable for thrombectomy⁸.
• Perfusion imaging, which shows blood flow, can identify salvageable brain tissue in people seen later or who wake with symptoms^2,8.
• MRI is used for many people with suspected TIA⁸.
• Heart tests such as an electrocardiogram (ECG) look for atrial fibrillation, and ultrasound scans can examine blood vessels in and around the brain⁹.

How scientists study it

Current treatments

Research frontiers

Living with the condition and seeking help

Emergency services should be called immediately if a stroke is suspected, even if the symptoms seem to have stopped, and the person should not be driven to hospital by car⁹. In India, the national emergency number is 112 and the ambulance number is 108^18,19. Rapid treatment saves brain tissue and lives^4,5.

Recovery varies widely. After discharge, a home recovery plan may include physiotherapy, therapy for speech, swallowing and vision, and support for anxiety, depression and fatigue, with a review of progress after about six months¹¹.

Carers play a major part in recovery and should seek support for themselves¹¹. Most strokes are linked to modifiable risks, so stopping smoking, staying active, eating well and treating high blood pressure reduce the chance of a first or repeat stroke³.