What is the TOAST (Trial of Org 10172 in Acute Stroke Treatment) classification for stroke?

TOAST Classification for Stroke

The TOAST (Trial of Org 10172 in Acute Stroke Treatment) classification divides ischemic stroke into five subtypes based on etiology: 1) large-artery atherosclerosis, 2) cardioembolism, 3) small-vessel occlusion, 4) stroke of other determined etiology, and 5) stroke of undetermined etiology.

TOAST Classification System Details

1. Large-Artery Atherosclerosis

• Clinical features: Cortical, cerebellar, or brainstem dysfunction
• Imaging: Infarct >1.5 cm in diameter
• Diagnostic criteria: >50% stenosis or occlusion of a major brain artery or branch cortical artery
• Supportive evidence: History of claudication, TIAs in same vascular territory, carotid bruits

2. Cardioembolism

• Clinical features: Sudden onset with maximum deficit at beginning
• Imaging: Usually cortical infarcts
• Diagnostic criteria: At least one cardiac source identified (e.g., atrial fibrillation, mechanical valve, recent MI)
• Supportive evidence: Previous TIA/stroke in different vascular territories

3. Small-Vessel Occlusion (Lacunar)

• Clinical features: Lacunar syndrome without cortical dysfunction
• Imaging: Subcortical infarct <1.5 cm in diameter
• Diagnostic criteria: History of diabetes or hypertension
• Exclusion criteria: Potential cardiac or large vessel sources

4. Stroke of Other Determined Etiology

• Clinical features: Variable based on cause
• Diagnostic criteria: Rare causes identified through specific testing (e.g., vasculitis, hypercoagulable states, dissection)
• Exclusion criteria: Common causes ruled out

5. Stroke of Undetermined Etiology

• Includes three subcategories:
  • Cryptogenic stroke: No cause identified despite extensive evaluation
  • Multiple potential causes identified
  • Incomplete evaluation

Clinical Application and Significance

The TOAST classification has significant implications for:

1. Treatment decisions: Different subtypes may respond differently to specific interventions 1. For example:

   • Cardioembolic strokes often require anticoagulation for secondary prevention
   • Large-artery atherosclerosis may benefit from antiplatelet therapy and possible revascularization

2. Prognosis determination: Stroke subtypes have different recurrence rates and outcomes 1

3. Research applications: Allows for standardized reporting in clinical trials 1

Limitations and Evolutions

Despite being the most widely used classification system, TOAST has some limitations:

• Moderate interrater reliability
• Up to 40% of strokes classified as "undetermined" 1
• Does not account for multiple potential causes

Newer classification systems have been developed to address these limitations:

• Causative Classification System (CCS): Web-based, automated system with improved reliability
• ASCOD Classification: Grades potential causes (Atherosclerosis, Small-vessel disease, Cardiac source, Other cause, Dissection) by degree of likelihood 2
• Chinese Ischemic Stroke Subclassification (CISS): Enhanced accuracy for Asian populations 3

Practical Implementation

When applying TOAST classification in clinical practice:

1. Obtain comprehensive vascular imaging (carotid/cerebral vessels)
2. Perform cardiac evaluation (echocardiography, rhythm monitoring)
3. Assess for hypercoagulable states in younger patients or those without traditional risk factors
4. Document certainty level ("probable" vs "possible")

Common Pitfalls to Avoid

• Incomplete workup: Recent data shows only 61% accuracy in TOAST classification in clinical practice 4
• Premature classification: Ensure adequate diagnostic testing before assigning a subtype
• Ignoring multiple mechanisms: Consider all potential contributing factors
• Overreliance on imaging alone: Clinical features should be integrated with imaging findings

The TOAST classification remains fundamental to stroke medicine despite newer systems, providing a standardized framework for categorizing stroke etiology that guides treatment decisions and research efforts.