Abstract DP107: Magnetic Resonance Imaging-Based Triage of Stroke Mimics: The Impact on Thrombolysis

Background and Purpose: Intravenous thrombolysis requires brain imaging prior to administration. Head CT (HCT) is most commonly used because it is fast, available, and provides data for treatment decisions. However, HCT cannot reliably diagnose ischemic stroke within the treatment window, so decisions rely on clinical candidacy (CC), leading to potential treatment of stroke mimics. MRI can exclude hemorrhage and confirm ischemic stroke, enabling triage based on disease candidacy (DC). The purpose of this study was to review a cohort of patients triaged using MRI to determine how their management would have differed under CC-based versus DC-based decision-making. Methods: Patients presenting to the ED with stroke-like symptoms within the thrombolysis window between July 2022–June 2023 were retrospectively analyzed. All underwent stroke protocol brain MRI as initial imaging. Blinded to outcomes, cases were reviewed for CC based on history and examination. Estimated treatment rates by CC were compared with actual rates, which were based on DC (MRI-positive stroke). It was assumed that patients with a negative MRI would also have a normal HCT. Cost implications were calculated using standard reimbursement benchmarks and real-world values. Results: A total of 190 patients were triaged with MRI. Of these, 101 presented within the treatment window, 82 had no contraindications, and 43 met clinical candidacy (CC). Of these 43 patients, who would have been eligible by HCT, only 13 had a stroke on MRI, meeting disease candidacy (DC). Thus, 70% of patients who met CC did not meet DC and may have received thrombolysis under HCT triage. Interrater agreement among 6 stroke neurologists who reviewed clinical vignettes representative of CC- positive cases was moderate (Fleiss’ kappa 0. 42), with 80% of mimics considered eligible for thrombolysis by at least one neurologist. Net cost savings from avoiding inappropriate thrombolysis were estimated at 510, 000–820, 000, even after accounting for increased MRI use. Conclusions: MRI-first triage appears to have greatly reduced the thrombolysis of stroke mimics, potentially preventing misdiagnoses, unneeded exposure to thrombolytics, and unnecessary admissions. These benefits need to be weighed against the potential delays in treatment caused by an MRI triage approach.