The article by Yoon et al. [1] reported that the eosinophil count and eosinophil cationic protein (ECP) have statistically insignificant predictive value for multiple allergen simultaneous test (MAST) positivity in chronic rhinosinusitis (CRS), with area under the curve (AUC) values below 0.6.

Building on their methodology, we analyzed a larger cohort of patients using similar criteria and methods. Our findings reveal that the results in CRS with nasal polyp (CRSwNP) group had minimal predictive value. In contrast, CRS without nassal polyps (CRSsNP) group showed statistically significant AUC values (eosinophil proportion [EO%] AUC=0.730, p=0.013; eosinophil count [EO count] AUC=0.710, p=0.024), as illustrated in the Fig. 1. This suggests that eosinophilic parameters may hold predictive value in CRSsNP when evaluated with larger sample sizes.

We hypothesized three potential reasons for the difference in the predictive value of eosinophilic markers between CRSwNP and CRSsNP:

1) Differences in inflammatory pathways: CRSwNP is primarily associated with type 2 inflammation, characterized by elevated levels of eosinophils, interleukins (IL-4, IL-5, and IL13), and IgE. In this type of inflammation, eosinophils may participate in a chronic inflammatory process that is independent of immediate allergen sensitization (MAST positivity). Conversely, CRSsNP typically exhibits non-eosinophilic or neutrophilic inflammation, whereas eosinophils might directly reflect an allergic response. This could explain why EO counts in CRSsNP correlate more closely with MAST positivity, indicating an allergic etiology, whereas in CRSwNP, eosinophils contribute to a broader, more complex inflammatory environment [2].

2) Tissue remodeling and barrier dysfunction in CRSwNP: CRSwNP is characterized by significant tissue remodeling, which includes fibrosis, epithelial damage, and the formation of polyps. This extensive tissue damage can disrupt the functioning of eosinophils and the exposure to allergens in the nasal mucosa, resulting in a weaker correlation between eosinophil counts and MAST positivity [3]. In contrast, patients with CRSsNP experience less severe tissue remodeling, which allows eosinophils to more accurately reflect local allergic sensitization. Therefore, in CRSwNP, the predictive value of eosinophil counts may be obscured by the extensive tissue changes.

3) MAST positivity reflects systemic allergy in CRSwNP, not local inflammation: In patients with CRSwNP, MAST positivity is likely indicative of systemic allergic sensitization rather than local eosinophilic inflammation. The increased eosinophil count observed in CRSwNP could stem from a broader type 2 immune response, rather than being a direct response to allergens identified by the MAST [4]. Consequently, eosinophils may not be reliable indicators of local allergic activity in CRSwNP, whereas in CRSsNP, they may more accurately reflect localized allergic inflammation.

We believe that the differences in findings between CRSwNP and CRSsNP populations may underscore the distinct roles of eosinophils in these conditions. Our results suggest that both eosinophil count and percentage could play a role in predicting MAST positivity in CRSsNP patients, although they appear to be less significant in CRSwNP.