Eosinophils, malignant brain edema, and functional outcome after mechanical thrombectomy: a mediation analysis

Objective To examine the independent associations of admission eosinophil count with malignant brain edema (MBE) and with poor 3-month functional outcome after mechanical thrombectomy (MT), and to quantify the statistical contribution of MBE to the eosinophil-outcome association using mediation analysis. Methods A total of 442 consecutive AIS patients who underwent MT between May 2017 and January 2023 were analyzed. Multivariable logistic regression analysis was used to assess the association of eosinophils with MBE and poor outcome. Mediation analysis was performed to quantify the statistical contribution of MBE. Results MBE developed in 98 (22.17%) patients. After full adjustment for confounders, each 1-standard deviation increase in standardized eosinophils was independently associated with a lower risk of MBE (OR = 0.165; 95% CI: 0.055–0.498; p = 0.00137). Consistent findings were observed when eosinophils were dichotomized by the median value (OR = 0.168; 95% CI: 0.086–0.328; p < 0.00001). Standardized eosinophils were also independently associated with reduced risk of poor outcome (OR = 0.620; 95% CI: 0.475–0.810; p = 0.00045). Mediation analysis showed a small statistical contribution of MBE to the eosinophil-outcome association: the indirect effect was −0.2109 (95% CI: −0.4016 to −0.0500; p < 0.001), and the mediated proportion was 12.05% (95% CI: 2.92–26%). Conclusion Lower admission eosinophil levels were independently associated with higher risks of MBE and poor 3-month functional outcome. Mediation analysis indicated that MBE statistically accounted for 12.05% (95% CI: 2.92–26%) of the eosinophil-outcome association. These findings are hypothesis-generating and require external multicenter validation.