Clinical, functional and inflammatory characteristics in patients with pauci-granulocytic stable asthma: comparison with different sputum phenotypes

Abstract

Background

According to induced sputum cell count, four different asthma phenotypes have been recognised(eosinophilic, neutrophilic, mixed and pauci-granulocytic). The aim of the present study was to detect functional and inflammatory characteristics of patients with pauci-granulocytic asthma.

Methods

240 asthmatic patients were categorised in the four phenotypes according to cell counts in induced sputum. All patients underwent pulmonary function tests, and measurement of FeNO. The levels of IL-8, IL-13, and ECP were also measured in sputum supernatant. Treatment, asthma control and the presence of Severe Refractory Asthma(SRA) were also recorded.

Results

Patients were categorized in the four phenotypes as follows: eosinophilic (40%), mixed (6.7%), neutrophilic (5.4%) and pauci-granulocytic (47.9%). Although ACT did not differ between groups (p=0.288) patients with pauci-granulocytic asthma had better lung function (FEV₁%pred) (median (IQR):71.5(59.0-88.75) vs 69.0(59.0-77.6) vs 68.0(60.0-85.5) vs 80.5(69.7-95.0), p=0.009] for eosinophilic, mixed, neutrophilic and pauci-granulocytic asthma respectively, p=0.009). SRA occurred more frequently in the eosinophilic and mixed phenotype (41.6% and 43.7% respectively) and less frequently in the neutrophilic and pauci-granulocytic phenotype (25% and 21.7% respectively, p=0.01). FeNO, ECP and IL-8 were all low in the pauci-granulocytic, whereas as expected FeNO and ECP were higher in eosinophilic and mixed asthma, while IL-8 was higher in patients with neutrophilic and mixed asthma(p<0.001 for all comparisons). Interestingly, 14.8% of patients with pauci-granulocytic asthma had poor asthma control.

Conclusion

Pauci-granulocytic asthma most likely represents a "benign" asthma phenotype, related to a good response to treatment, rather than a "true" phenotype of asthma. However, pauci-granulocytic patients that remain not-well-controlled despite optimal treatment represent an asthmatic population that requires further study for potential novel targeted interventions.

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