Abstract
In the recent years the attention of researchers has been focused on identifying approaches to the differentiation of asthma phenotypes, which is especially important in the case of severe asthma (SA).
The aim of the study was to identify SA phenotypes.
Methods. Hierarchical cluster analysis was used to identify asthma phenotypes in 63 patients with SA.
Results. The most adequate model was obtained using a combination of such parameters as allergic status, frequency of exacerbations, postbronchodilator FEV1 and mean variability of PEF. Two phenotypes of SA were identified in this model. 38 patients with predominantly nonallergic asthma and severe airway obstruction were assigned to cluster 1 (phenotype of SA with irreversible airway obstruction), and 25 patients with predominantly allergic asthma, high frequency of exacerbations and significant PEF variability, but with less pronounced airway obstruction - to cluster 2 (phenotype of severe labile asthma).
The patients from cluster 1 demonstrated the presence of lung hyperinflation (higher RV/TLC than in cluster 2: 140,7 (125,3-161,6) %pred vs 121,7 (117,0-133,8) %pred, ?=0,005). Sputum neutrophil count was higher in cluster 1 than in cluster 2 (28 (22-31)% vs 18 (17-24)%, ?=0,005). Level of neutrophils in sputum in this group correlated with FEV1/FVC (rs=-0,69, p=0,009), that may indicate the involvement of neutrophilic inflammation in the development of irreversible obstruction. The serum level of IL-8 (which is known to be a chemoattractant for neutrophils) was higher in cluster 1 than in cluster 2 (57 (25-101) pg/ml vs 15 (10-55) pg/ml, p=0,015).
Conclusion. The possibility of identification of two distinct phenotypes of SA using cluster analysis was demonstrated.