The Determinants of Eosinophilia in Patients With Severe Asthma

Asthma is defined by the Global Initiative for Asthma (GINA) as a heterogeneous disease characterized by chronic airway inflammation. The pathogenesis of the disease is better understood with the comprehension of immunological pathways. These pathways differ by the type of recruited cells and released interleukin (IL). Thus, asthma can be classified into subtypes based on the underlying immune mechanism: eosinophilic asthma (EA) and non-eosinophilic asthma (NEA). Patients with EA tend to respond better to inhaled corticosteroid as compared to those with NEA. The distinction of EA is very important in the light of emergent type 2 inflammation targeted therapies.

We performed a 1-year (2018) retrospective cohort analysis of the Nationwide Inpatient Database (NIS). We included all adult patients presenting with severe asthma. Patients were stratified into two groups: eosinophilic severe asthma and non-eosinophilic severe asthma. The primary outcomes measures were the prevalence of chronic steroid use, status asthmaticus, family history of asthma, food, drug and environmental allergies, presence of nasal polyps, allergic rhinitis, allergic dermatitis, need for mechanical ventilation, need for oxygen supplementation, gastroesophageal reflux disease, in-hospital mortality, and length of stay. We performed descriptive statistics. Continuous parametric variables were reported using a mean and standard deviation. Continuous nonparametric variables were reported using a median and interquartile range. To compare the characteristics of the two groups, we used the independent t-test for continuous parametric variables and the Mann-Whitney U test for continuous nonparametric variables. The Chi-square test was used to assess differences in categorical variables.

A total of 2,646 patients were included, out of which 882 belonged to the eosinophilic group and 1,764 were in the non-eosinophilic group. Comparing EA versus NEA, we have found that eosinophilic group was characterized by higher percentage of steroid use (18.3% vs. 9.5%, P < 0.001). This group also had higher rates of status asthmaticus and positive family history (P = 0.009 and 0.004, respectively). The presence of allergies, allergic rhinitis, nasal polyps, and allergic dermatitis was higher among patients with eosinophilia. The need for mechanical ventilation and supplemental oxygen was also higher among this group (P < 0.001 for both); however, there was no significant difference in mortality rate (P = 0.347) and the length of hospital stay was similar in both groups (P < 0.001).

We showed herein that the eosinophilic subtype of asthma differs widely from the non-eosinophilic phenotype. Clinically, patients with eosinophilia might exhibit different symptomatology, more atopy, and concomitant comorbidities. However, this group might have better response to steroid therapy and might benefit from the new emergent T2 immune targeted therapy. The identification of EA is crucial for better disease control.