Why use it

ASCOD provides more granular and transparent stroke phenotyping than TOAST. It explicitly quantifies diagnostic uncertainty, identifies all coexisting vascular risk factors and pathologies, and guides secondary prevention. It is recommended by the European Stroke Organisation and used in major international stroke registries and clinical trials.

About

The ASCOD grading system is a comprehensive etiological classification for ischemic stroke and TIA. Unlike TOAST (which assigns a single cause), ASCOD assigns a probability grade to each of five pathological domains: A = Atherosclerosis, S = Small vessel disease, C = Cardiac source, O = Other cause, D = Dissection. Each domain is graded 1 (directly causal), 2 (causal association uncertain), 3 (disease present but unlikely causal), 0 (disease absent), 9 (workup insufficient). ASCOD acknowledges that multiple etiologies may coexist and that uncertainty is the norm in stroke diagnosis.

When to use

Comprehensive etiological workup of any ischemic stroke or TIA
After completing appropriate diagnostic evaluation (MRI/MRA, echocardiography, cardiac monitoring, vascular imaging)
Research classification and stroke registry documentation
Guiding secondary stroke prevention strategy based on dominant etiology

Formula

Five domains, each graded independently: A (Atherosclerosis): Extracranial/intracranial large artery atherosclerosis S (Small vessel disease): Lacunar infarct with or without white matter disease C (Cardiac source): AF, valvular disease, cardiomyopathy, etc. O (Other cause): Hypercoagulable state, vasculitis, genetic, etc. D (Dissection): Carotid or vertebral artery dissection Grading per domain: 1 = Directly causal (disease present AND compatible stroke mechanism) 2 = Uncertain causal association (disease present, unclear causality) 3 = Disease present but unlikely causal for this stroke 0 = Disease absent (negative workup) 9 = Workup insufficient to assess this domain

Pearls & pitfalls

Unlike TOAST, ASCOD is not mutually exclusive — a patient can have simultaneous A2/S1/C2.
Grade 1 means the disease is directly causal; grade 2 means causal but uncertain; grade 3 means present but uninformative.
Grade 9 (workup insufficient) should trigger completion of the relevant evaluation, not permanent classification.
Dissection (D domain) is critically important in young stroke patients (<50y) — always consider.
Cardiac monitoring for ≥72h is needed to adequately assess C domain (AF detection).
The ASCOD phenotype directly informs antiplatelet vs. anticoagulation vs. revascularization strategies.

Next steps

Grade 1 in any domain = direct causal attribution → guide secondary prevention accordingly. Grade 2 in a domain = further workup warranted (e.g., prolonged cardiac monitoring, repeat vascular imaging). Grade 9 = workup incomplete → complete evaluation urgently. Combined grade 1 in multiple domains = competing etiologies (e.g., A1/C1) → treat both.

Evidence

Amarenco P et al. (Stroke 2013) introduced ASCOD. Validated in TIAregistry.org (>4,000 patients). Shown to have better inter-rater reliability than TOAST for specific subtypes. ESO endorsed as a reference classification system.

References

Amarenco P et al. The ASCOD phenotyping of ischemic stroke (Updated ASCO Phenotyping). Cerebrovasc Dis. 2013;36(1):1-5. — link
Amarenco P et al. The ASCO (phenotyping) classification of stroke. Cerebrovasc Dis. 2009;27(5):502-508. — link

ASCOD Algorithm for Ischemic Stroke

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