Mechanical thrombectomy (MT) for large vessel occlusion (LVO) ischemic stroke is a safe and effective treatment modality. The National Institute of Health Stroke Scale (NIHSS) 24 h after MT (24 h-NIHSS) was shown to serve as the strongest surrogate for 90-day functional outcome. Here, we seek to externally validate 24 h-NIHSS as predictor for 90-day functional outcome and explore additional variables in this context.
Patients treated for anterior LVO between February 2016 and August 2020 with premorbid mRS < 3 were included. Receiver operating characteristics were used to compare different NIHSS-related surrogates, such as baseline (B) NIHSS, 24 h-NIHSS, Δ‑NIHSS and percent (%) change NIHSS to predict favorable function outcome (mRS 0-2). Additional analysis was performed to assess predictors associated with poor outcome despite reaching the best predictor threshold.
A total of 337 eligible cases were identified. The 24 h-NIHSS outperformed B‑NIHSS, Δ‑NIHSS, and %‑NIHSS in terms of 90-day mRS 0-2 prediction. A 24-NIHSS ≤ 8 was identified as the optimal binary threshold. Multivariable analysis demonstrated that 24-NIHSS ≤ 8 and younger patient age were independently associated with mRS 0-2. Despite achieving 24 h-NIHSS ≤ 8, 23/143 (16.1%) cases experienced poor outcome (mRS 4-6). Older age, higher baseline NIHSS, coexisting chronic kidney disease, and longer hospital stay were independent predictors for poor outcome despite achieving 24 h-NIHSS ≤ 8.
An NIHSS of 8 or less 24 h after MT was validated to serve as an independent, strong surrogate for favorable functional outcome; however, cofactors such as older age, higher baseline NIHSS and coexisting comorbidities appear to mitigate this clinical adjunct.

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