Transient ischaemic attack

Traditionally, when magnetic resonance imaging (MRI) was less readily available, the definition of transient ischaemic attack (TIA) was based on time (ie an episode of focal neurological dysfunction, with an abrupt onset, that lasted less than 24 hours and had a vascular cause). Often, after an apparent TIA, the patient has signs of brain infarction on MRI even though their symptoms resolve. As a consequence, the definition of TIA has become less strictly based on time, with greater emphasis on whether the patient has had an infarct. An episode is considered to be a:

• mild stroke if brain infarction is identified
• TIA if symptoms resolve completely within 24 hours and there is no brain infarction.

The risk of a stroke after a TIA is about 10% at 2 weeks, and half these events occur within 48 hours. This emphasises the need for rapid clinical assessment and investigations (see advice).

Factors associated with an increased risk of subsequent stroke include age older than 60 years, raised blood pressure (more than 140/90 mmHg), motor or speech symptoms, symptoms that last longer than 1 hour, and diabetes. At greatest risk are patients with established infarction on brain imaging, atrial fibrillation or a high-grade symptomatic carotid stenosis.

The causes and management of TIA are similar to acute ischaemic stroke. All patients with a TIA should start taking aspirin (see drug advice) and follow other secondary prevention measures.