In the DAWN trial, mechanical thrombectomy for ischemic stroke was extended to 24 hours from symptom onset. What selection criterion was used (beyond clinical-imaging mismatch) to identify eligible patients?

• A Any NIHSS score >6 regardless of imaging findings
• B CT angiography showing collateral score ≥2 on 10-point scale
• C Time from last known well >24 hours with normal CT
• D Clinical-diffusion MRI mismatch (large NIHSS deficit with small infarct core on diffusion-weighted MRI) ✓

Explanation

The DAWN trial (NEJM 2018) enrolled patients with occlusion of ICA or M1 segment between 6–24 hours of last known well, selecting by clinical-core mismatch — NIHSS ≥10 with infarct core <31 mL (or NIHSS ≥20 with core <51 mL by DWI/CT perfusion). This 'tissue window' approach selects patients with a large penumbra despite a small infarct core, who benefit from late reperfusion. NIHSS alone without imaging mismatch is insufficient. Collateral scoring was used in ESCAPE trial, not DAWN.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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