4 Discussion
Blood eosinophil is a crucial biomarker which is in connection with specific endotype and severity of CRSwNP(11, 17). Our previous study has demonstrated that systemic eosinophilia (Blood eosinophil count ≥0.3×109/L) were associated with poor treatment outcome of nasal polyps(5). However, the correlation of paranasal sinus CT features and blood eosinophil count was rarely observed in the previous study. Thus, identification of auxiliary clinical parameters strongly linked to blood eosinophilia in CRSwNP could be helpful to assess the prognosis and guide the management. The new finding in the present research is that OC score was positively related to the level of blood eosinophil, and an independently predictor for systemic eosinophilia of nasal polyps. Overall, these results indicate that olfactory cleft opacification in paranasal sinus CT scan could be a feature for the phenotype of CRSwNP with blood eosinophilia.
In this study, the percentage of subjects with blood eosinophilia was 40% while 60% was subjects without blood eosinophilia based on the cutpoint of 0.3×109/L. Nevertheless, the consensus about the cutpoint of blood eosinophilia in CRSwNP has not reached. The results about significant difference in clinical characteristics between two subgroups confirm that eosinophilic inflammation in blood is linked to the comorbidities such as allergy rhinitis and asthma and poor disease control as well, which are in accordance with previous studies(5). Although it is not clear that how blood eosinophilia acts on the pathogenesis of CRSwNP, we could speculate that systemic eosinophilia may contribute to local eosinophilic infiltration in nasal mucosa and relate to structured histopathology in nasal polyps (18, 19).
In clinical practice, blood routine examination is the most direct method that reflect the status of eosinophilic inflammation in blood. However, the count of peripheral blood eosinophil is largely affected by oral glucocorticoid treatment (20, 21). Therefore, finding additional parameters correlated to systemic eosinophilia is necessary. Paranasal sinus CT scan as a widely used and noninvasive test has been used to identify the phenotypes of CRSwNP(7), predict the recurrence(10) and assess the sensitivity of glucocorticoid for the patients(22). but few studies concentrate on the relationship between paranasal sinus CT features and peripheral systemic eosinophilia. Interestingly, our study showed that OC score, PES score, ES score, SS score, ES/MS ratio and PES/AES ratio were higher in the B-high subgroup, but only OC score as the independent risk factor was associated with systemic eosinophilia. And for all we know, this is the first research for reporting the significant correlation between OC area opacification in paranasal sinus CT scan and CRSwNP with systemic eosinophilia.
Previous study has verified that olfactory cleft opacification were associated with olfactory dysfunction(23, 24), and could be a clinical predictor for identifying eosinophilic CRS(25). Chen et al. (16)have confirmed that OC score could be used to identify the airway hyperresponsiveness in CRS, which is positively associated with blood eosinophil counts. These reports indicated that OC score was related to systemic eosinophilia in CRSwNP. Although the reason why OC scores were higher in the patients with systemic eosinophilia is unclear, the finding in this study suggests that the area of olfactory cleft with opacification could be sensitive to the eosinophilic inflammation in the blood.
However, several limitations in our present study are worth considering. The size of sample size was small, and the data in this research were short of validation in prospective cohort study. In addition, the patients in the retrospective cohort were derived from a single tertiary medical center, which may be not generalizable to patients with CRSwNP in other medical institutions. Finally, 22-item Sinonasal Outcome Test score as a clinical parameter was not included for the assessment of disease severity.
To sum up, our study reveals that OC opacification in sinus CT is independently associated with blood eosinophilia, and may be served as a specific indicator of systemic eosinophilia in CRSwNP patients.