ABSTRACT NUMBER: ESOC2026A2000 CLINICAL OUTCOME OF MRI-NEGATIVE ACUTE ISCHEMIC STROKE TREATED WITH AND WITHOUT INTRAVENOUS THROMBOLYSIS

Abstract Background and aims Intravenous thrombolysis (IVT) for acute ischemic stroke (AIS) is guided by clinical assessment and exclusion of radiological contraindications. While MRI protocols reduce mistreatment of stroke mimics, infra-radiologic strokes (IRS) on admission MRI remain diagnostically challenging. We aimed to characterize MRI-based IRS and evaluate their clinical and functional outcomes. Methods From our local prospectively-constructed stroke registry we identified all AIS undergoing acute MRI, without intracranial occlusion. IRS were defined as clinically diagnosed AIS with negative DWI and perfusion imaging. IRS were compared with radiologically confirmed (RC)-AIS. Within IRS-patients, IVT-treated patients were compared with those receiving conservative treatment. Outcomes included 3-month modified-Rankin-Scale (mRS) shift, 24-hour-NIHSS-shift, lesion evidence on follow-up imaging (LFI). Analyses were adjusted using propensity score weighting. Results Among 1,315 consecutive eligible AIS between 2018 and 2024, 58 (4.4%) had an IRS. Compared with RC-AIS in univariate analysis, IRS patients had similar baseline NIHSS, shorter onset-to-door times (96 vs. 246 min, p<0.001), less paresis (44.8% vs. 63.4%, p=0.006), more infra-tentorial localization (48.3% vs. 22.5%, p<0.001), received more IVT (63.8% vs. 32.1%, p<0.001), and had less LFI (17.8% vs. 73.3%, p<0.001). After adjustment, IRS patients had greater 24-hour-NIHSS improvement (beta=1.68, 95%CI=0.29-3.07), less LFI (pswOR=0.05, 95%CI=0.02-0.12), and similar 3-month mRS. Within the IRS group, IVT was associated with greater 24-hour-NIHSS improvement (beta=2.97, 95%CI=1.17-4.78) without significant 3-month mRS changes. Conclusions IRS represent an uncommon AIS radiotype and overall similar medium-term outcomes as MRI-positive AIS. In IRS, IVT was associated with improved short but not medium-term outcomes. Conflict of interest François Fenter: nothing to disclose. Vincent Dunet: nothing to disclose. Patrik Michel: nothing to disclose. Davide Strambo: advisory board for Boehringer Ingelheim. Figure 1 - belongs to Results