Definition of Transient Ischemic Attack (TIA)
A transient ischemic attack (TIA) is a brief episode of neurological dysfunction caused by a focal disturbance of brain or retinal ischemia, with clinical symptoms typically lasting less than 1 hour, and without evidence of infarction. 1
Evolution of the TIA Definition
The traditional time-based definition of TIA described it as "rapidly developed clinical signs of focal or global disturbance of cerebral function lasting fewer than 24 hours, with no apparent non-vascular cause" 1
With the advancement of modern brain imaging techniques, this definition has evolved, as many patients with symptoms lasting less than 24 hours are found to have evidence of brain infarction 1
The newer tissue-based definition emphasizes:
- Brief duration (typically less than 1 hour)
- Absence of infarction on imaging
- Focal nature of the disturbance 1
Clinical Characteristics of TIA
TIAs manifest as transient focal neurological deficits that may include:
- Unilateral limb weakness
- Speech disturbances
- Sensory symptoms
- Visual disturbances (including monocular blindness)
- Gait difficulties 2
Some symptoms are more specific to TIAs than strokes:
- Monocular blindness is more common in TIA than stroke
- Limb shaking occurs almost exclusively in TIA patients 2
Clinical Significance
TIAs are important warning signs and powerful risk factors for subsequent stroke 3
The risk of stroke following a TIA is substantial:
- 8.8% at 7 days
- 11.6% at 90 days 1
In patients with symptomatic carotid disease, the 90-day risk of ipsilateral stroke rises to 20.1% 1
The greatest stroke risk appears within the first week after a TIA 1
Diagnostic Approach
Modern imaging plays a crucial role in differentiating TIA from stroke:
- Absence of acute infarction on brain imaging is essential for TIA diagnosis
- CT or MRI can identify patients with infarction despite transient symptoms 1
CT perfusion can identify abnormalities in up to one-third of TIA cases, which may help with risk stratification 1
Vascular imaging of the cervical carotid arteries is important, particularly for carotid territory TIAs, as the degree of stenosis correlates with stroke risk 1
Common Pitfalls in TIA Diagnosis
Several conditions can mimic TIA symptoms but are not caused by cerebrovascular disease (TIA mimics) 2
Syndromes that are uncommon manifestations of cerebral ischemia include:
- Isolated dizziness
- Syncope
- Drop attacks
- Global amnesia 4
Careful history, examination, and appropriate imaging are needed to differentiate true TIAs from mimics 2
Clinical Implications
TIA should be considered a medical emergency requiring urgent evaluation and treatment 5
The recognition of TIA provides an excellent opportunity for stroke prevention that is often missed or poorly recognized 3
Risk stratification tools can help identify patients at highest risk for subsequent stroke 5
Patients with TIA have a one-third risk of recurrent TIAs and one-third risk of eventual stroke 6