What is the definition of a transient ischemic attack and what are the recommended immediate diagnostic and therapeutic measures?

TIA Definition and Management

Definition of Transient Ischemic Attack

A TIA is defined as a transient episode of neurological dysfunction caused by focal brain, spinal cord, or retinal ischemia, without acute infarction on imaging. 1

The definition has evolved significantly from the traditional time-based criterion:

• Traditional definition: Focal neurological symptoms lasting <24 hours 1
• Modern tissue-based definition: Brief neurological dysfunction (typically <1 hour) caused by focal ischemia without evidence of infarction on imaging 1, 2
• The shift occurred because up to one-third of patients with symptoms <24 hours show infarction on modern brain imaging, making them strokes rather than TIAs 1

Retinal TIA (amaurosis fugax) is formally recognized as a stroke equivalent by the American Heart Association, manifesting as acute, transient, painless monocular vision loss from temporary retinal artery occlusion 2

Critical Stroke Risk After TIA

TIA is a medical emergency with the highest stroke risk in the first week. 1, 2

The stroke risk stratification is:

• 2 days: 1.36-3.6% 2
• 7 days: 2.06-11% (without urgent treatment) 2, 3
• 90 days: 2.78-17% 1, 2
• Symptomatic carotid stenosis ≥50%: 20.1% at 90 days 2, 3

Additional critical findings:

• Up to 31% of retinal TIA patients have silent cerebral infarctions on diffusion-weighted MRI despite no neurological symptoms 2
• Acute coronary syndrome occurs in 5.4% at one year, indicating systemic vascular instability 2

Immediate Diagnostic Measures

All TIA patients require urgent evaluation within 24-48 hours, ideally in an emergency department setting. 1, 2, 3

Brain Imaging (Required)

• CT or MRI within 24-48 hours to distinguish ischemic from hemorrhagic events and detect infarction 1, 3
• Diffusion-weighted MRI is preferred as it identifies infarction in >25% of clinically-defined TIAs 3
• CT perfusion may reveal abnormalities in up to one-third of TIA cases for risk stratification 2, 3

Vascular Imaging (Essential)

• Carotid ultrasound, CTA, or MRA to evaluate for carotid stenosis, which is present in up to 40% of retinal TIA patients 1, 2, 3
• Ipsilateral carotid stenosis ≥70% is found in up to 40% of retinal TIA patients 2
• Vascular imaging of cervical carotid arteries is critical because stenosis degree correlates directly with stroke risk 2, 3

Cardiac Evaluation (Mandatory)

• 12-lead ECG to identify atrial fibrillation or other arrhythmias as cardioembolic sources 3
• Atrial fibrillation prevalence ranges 6-20% in TIA patients 2
• Echocardiography (transthoracic or transesophageal) when cardioembolic mechanism is suspected, especially in patients <45 years 3

Laboratory Studies

• Basic metabolic panel, CBC, renal function, fasting glucose, lipid panel to identify modifiable risk factors 3
• Coagulation studies (INR, aPTT) if bleeding disorder suspected or patient on anticoagulation 3

Clinical Features to Document

Recording the exact time of symptom onset (last known well) is the single most critical piece of information for risk stratification. 3

Distinguishing TIA from Seizure Mimics

• Negative motor phenomena (weakness, numbness, vision loss) indicate TIA because they reflect loss of function in a vascular territory 3
• Positive motor phenomena (limb shaking, jerking, tonic posturing) suggest seizure activity 3
• Todd's paralysis (post-seizure weakness) can mimic stroke but is preceded by seizure activity 3
• Post-ictal confusion or altered consciousness following deficit points toward seizure 3
• Symptoms following vascular-territory distribution (anterior carotid or posterior vertebrobasilar patterns) support TIA diagnosis 3

NIH Stroke Scale

• Perform NIH Stroke Scale for quantitative deficit measurement and monitoring 3
• Obtain EEG when seizures suspected based on positive motor phenomena or post-event confusion 3

Immediate Therapeutic Measures

Risk Factor Identification

The most prevalent modifiable risk factors requiring immediate attention:

• Hypertension: 57-77% prevalence 2
• Hyperlipidemia: 23-74% prevalence 2
• Diabetes: 14-61% prevalence 2
• Atrial fibrillation: 6-20% prevalence 2

Hospitalization Criteria

Hospitalization is recommended for patients with first TIA within 24-48 hours, especially with: 3

• Crescendo TIA
• Symptom duration >1 hour
• Symptomatic carotid stenosis >50%
• Known cardiac embolic source
• Hypercoagulable state

Urgent Interventions

• Early carotid revascularization should be considered if significant carotid stenosis identified, as benefit of carotid endarterectomy decreases considerably after 2 weeks from symptom onset 3
• Initiate appropriate antiplatelet therapy 4
• Blood pressure control, diabetes management, smoking cessation, and lipid management 3

Common Pitfalls

Do not attempt further testing in the ophthalmology office for retinal TIA—triage immediately to emergency department. 2

Do not delay vascular imaging even when seizure etiology is suspected, as seizures and cerebrovascular disease frequently coexist in elderly patients with vascular risk factors 3

Both TIA and ischemic stroke patients must have evaluation sufficient to exclude high-risk modifiable conditions such as carotid stenosis or atrial fibrillation. 1