Transient ischaemic attack: definition and difference from stroke
A transient ischaemic attack (TIA) is a passing episode of loss of function in one part of the brain from a temporary shortage of blood flow, with no infarction.
Remember
A TIA recovers completely, with no infarction on imaging, whereas an ischaemic stroke usually leaves a lasting deficit with infarction; a TIA also warns that a full stroke may follow soon.
Memory aid
a TIA is a stroke that cleared itself
Use it to recall that the blockage clears before the tissue dies, so the symptoms pass.
A transient ischaemic attack (TIA, often called a mini-stroke) is a short episode of focal neurological dysfunction. Transient means it passes. Focal neurological dysfunction means a loss of function in one part of the nervous system, such as one-sided weakness or speech disturbance, and here it comes from ischaemia, a short-lived shortage of blood flow to part of the brain.
What separates it from a stroke is the outcome: whether brain tissue dies. At the start the two can look identical, with the same arm weakness and slurred speech. In a TIA the blocked artery clears before brain tissue dies, so there is no infarction, which is death of brain tissue from lack of blood supply. In an established ischaemic stroke the deficit, a loss of function, is usually persistent because brain tissue has died.
Older teaching required recovery within 24 hours. The definition is now tissue-based: if an MRI scan shows a dead patch, even after a short episode, the event is classed as a stroke. Most TIAs last only minutes, and under an hour is usual. A deficit that lasts longer than about an hour is often accompanied by infarction, so it may be a stroke rather than a TIA.
A TIA has the same causes as an ischaemic stroke, such as a clot from the heart or from a narrowed artery in the neck. It matters because it is a warning. The risk of a full stroke is highest in the first 24 to 48 hours, so someone who feels well again still needs urgent specialist assessment.
Key facts
- Definition
- a brief focal ischaemic episode that recovers completely and leaves no acute infarction on imaging.
- Stroke
- an ischaemic stroke usually leaves a lasting deficit with infarction, whereas a TIA recovers completely.
- Timing
- symptoms usually clear within an hour, but the definition now depends on imaging rather than a fixed time limit.
- Causes
- the same as ischaemic stroke, such as a clot from the heart or from a narrowed neck artery.
- Imaging
- it excludes haemorrhage (bleeding) and shows whether any infarction (dead brain tissue) has formed.
- Urgency
- a warning of stroke, with the risk highest in the first 24 to 48 hours, so urgent specialist assessment is needed.
Exam traps
- Under 24 hours does not make an event a TIA. That is the old time-based definition, and under the tissue-based definition an episode with acute infarction on imaging is a stroke, not a TIA.
- A blocked artery supplying the brain (a cerebral artery) does not separate a TIA from a stroke, because a clot can block it in both. In a TIA the blockage is temporary and flow returns before tissue dies.
- Low blood glucose can cause a reversible focal deficit and must be excluded when a TIA is suspected. It is a mimic, meaning it can resemble a TIA, but a TIA is caused by focal ischaemia.
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