Stroke Severity and Functional Benefit of Thrombectomy in Acute M2 Middle Cerebral Artery Occlusion

BACKGROUND AND OBJECTIVES: Recent randomized trials reported no overall functional benefit of endovascular treatment (EVT) for distal medium-vessel occlusion (DMVO) and did not identify consistent effect modifiers to guide patient selection. Consequently, the role of EVT-particularly for M2 occlusions-remains controversial. We investigated whether baseline clinical severity modifies the association between successful recanalization and 90-day outcome in patients with M2 occlusion. METHODS: Multicenter retrospective cohort study at 2 tertiary stroke centers including consecutive adults with acute ischemic stroke due to M2 occlusion (January 2015-January 2023) triaged by multimodal CT and treated with EVT. The primary end point was functional independence (modified Rankin Scale [mRS] ≤ 2) at 90 days. Secondary end points included symptomatic intracerebral hemorrhage (sICH), mRS 0-1, and penumbra salvage volume (PSV). The primary analysis used multivariable logistic regression with baseline National Institutes of Health Stroke Scale (NIHSS) modeled linearly and an NIHSS×recanalization (modified Thrombolysis in Cerebral Infarction [mTICI] ≥2b) interaction term. Johnson-Neyman probing and inverse probability weighting (IPW) were applied; a supplementary restricted cubic spline analysis was performed to explore potential nonlinearity. RESULTS: = 0.42). DISCUSSION: In M2 occlusions, the magnitude of the association between successful recanalization and functional independence was larger at higher NIHSS and not reliably demonstrable at lower NIHSS. These findings support a severity-informed, individualized EVT approach while remaining hypothesis-generating rather than prescriptive for specific NIHSS thresholds. Major limitations include the retrospective observational design and potential residual confounding.