ABSTRACT NUMBER: ESOC2026A1507 PREDICTORS OF UNFAVOURABLE FUNCTIONAL OUTCOME DESPITE EARLY NEUROLOGICAL IMPROVEMENT AFTER MECHANICAL THROMBECTOMY

Abstract Background and aims Early neurological improvement (ENI) at 24 hours is a robust predictor of favourable outcome after mechanical thrombectomy (MT). However, some patients fail to achieve functional independence despite ENI. We aimed to identify predictors of unfavourable outcome defined as a modified Rankin Scale (mRS) 3-6 in patients with stroke exhibiting ENI. Methods We analysed data from a national registry of endovascular treatment (2015-2022). Inclusion criteria were: anterior circulation stroke, MT and ENI (defined as NIHSS reduction of 4 points or NIHSS 0-1 at 24 hours). Patients with pre-stroke mRS>2 were excluded. The primary outcome was 90-day unfavourable functional outcome (mRS 3-6). Multivariable logistic regression was used to identify independent predictors. Results Of 10936 eligible patients, 6234 (57%) showed ENI. Among these, 1122 (18%) had an unfavourable outcome at 90 days. In multivariable analysis, independent predictors of poor outcome despite ENI included: Age >75 years (aOR 2.8, 95%CI 2.1-3.6), Diabetes Mellitus (aOR 1.6, 95%CI 1.3-1.9), Symptomatic Intracranial Haemorrhage (sICH) (aOR 4.5, 95%CI 2.8-7.1), and longer Last-Known-Well-to-Puncture time (aOR 1.1 per hour). Successful reperfusion with a modified Thrombolysis in Cerebral Infarction (mTICI) of 3 was protective against 90-day unfavourable outcome (aOR 0.6, 95%CI 0.5-0.8). Intravenous thrombolysis showed no interaction with 90-day outcome. Conclusions Nearly one in five patients with ENI failed to achieve functional independence. Advanced age, diabetes, sICH, and delayed treatment were strong predictors of futile early recovery. These findings suggest that 24-hour NIHSS improvement, while valuable, may not fully capture long-term disability in high-risk patients. Conflict of interest The authors report no disclosures