Background and Purpose—Predictive models of outcome after ischemic stroke have incorporated acute diffusion-weighted MRI (DWI) information with mixed results. We hypothesized that serial measurements of DWI infarct volume would be predictive of functional outcome after ischemic stroke.

Methods—The prospective Acute Stroke Accurate Prediction (ASAP) Study included a prespecified serial imaging subgroup who underwent DWI studies at baseline (<24 hours after symptom onset) and Day 5 (±2 days). DWI infarct volumes were calculated using the Analyze software (Rochester, Minn). Clinical outcomes were assessed at 3 months. Univariate and multivariable regression analysis was performed to assess the relationship between change in DWI lesion volume and excellent neurological outcome (modified Rankin Scale 0, 1, and Barthel Index 95).

Results—In total, 169 cases from the ASAP study had serial DWI scans with a measurable lesion at baseline, follow-up, or both. The median baseline National Institutes of Health Stroke Scale score was 6 (interquartile range, 3 to 13). For each 10 cm³ of growth in DWI infarct volume, the OR for achieving an excellent outcome by modified Rankin Scale was 0.52 (95% CI, 0.38 to 0.71) and for the Barthel Index was 0.64 (95% CI, 0.51 to 0.79). Adjusting for clinically important covariates, the OR for an excellent modified Rankin Scale outcome was 0.57 (95% CI, 0.37 to 0.88) and excellent Barthel Index outcome was 0.75 (95% CI, 0.56 to 1.01).

Conclusions—Based on these data, the likelihood of achieving an excellent neurological outcome diminishes substantially with growth in DWI infarct volume in the first 5 days after ischemic stroke of mild to moderate severity.