PURPOSE: The modified Rankin Scale (mRS) at 90 days is the primary outcome in most acute stroke studies, but the long follow-up period has disadvantages. The National Institutes of Health Stroke Scale (NIHSS) at 24 h shows a strong, but imperfect, association with 90-day mRS. This study examines the association between 24-hour NIHSS and 90-day mRS and reasons for discrepancies. METHODS: Data are from the ESCAPE-NA1 thrombectomy patients. To address the non-normality distribution of the NIHSS and include deceased patients, a 7-point ordinal score was generated by grouping 24-hour NIHSS. The association of ordinal 24-hour NIHSS and 90-day mRS was assessed with adjusted ordinal logistic regression. Differences in baseline and treatment/post-treatment variables were compared between patients with discordant and concordant outcomes. RESULTS: One-thousand-seventy-six patients with available 24-hour NIHSS and 90-day mRS were included (median 24-hour NIHSS 6[IQR: 2-14], median 90-day mRS 2[IQR: 1-4]). Ordinal 24-hour NIHSS was associated with 90-day mRS (adjusted cOR 2.53 [95%CI 2.33-2.74]). Forty-eight (4.5%) patients had discordant outcomes. Of those, 19(1.8%) had 24-hour NIHSS <
6 and 90-day mRS5-6
all of which had ≥ 1 severe adverse event, most commonly pneumonia (6[31.6%]) or recurrent stroke (4[21.1%]). Twenty-nine patients (2.7%) had 24-hour NIHSS >
14 and 90-day mRS 0-2. In these patients, baseline NIHSS and ASPECTS was lower, and collateral status was worse. CONCLUSION: An ordinal NIHSS score that includes death at 24 h shows a strong association with 90-day mRS, suggesting that it could be used as an alternative outcome. Patients with discrepant outcomes differed from the remaining patients regarding their baseline NIHSS, ASPECTS, collateral status, and post-stroke complications.