Eosinophilic phenotype not definitive for steroid-therapy response
MedWire News: The use of inhaled corticosteroid therapy (ICS) might lead to the misclassification of asthma phenotypes, research shows.
"The inflammatory cell phenotypes reported in previous studies may therefore be inaccurate, influenced by the effects of steroid exposure and smoking," report Robin Taylor (University of Otago, New Zealand) and colleagues in the journal Thorax.
There are four subtypes of asthma phenotypes, based on the presence or absence of sputum eosinophils and/or neutrophils. A simpler classification lists two categories, eosinophilic (EA) or non-eosinophilic asthma (NEA). Steroid therapy is known to benefit EA, but the evidence is mixed regarding NEA.
Despite the classification of asthma, several factors might influence the accuracy of induced sputum cell types and therefore phenotype classification, according to the researchers. ICS therapy, as well as smoking, may influence inflammatory cell phenotypes, but there is also suggestions the cell phenotypes might change over time.
Taylor and colleagues assessed the inflammatory cell phenotypes in asthma after eliminating these potentially confounding effects and compared the response to steroids in EA and NEA.
After withdrawing ICS therapy in 94 patients with airway hyper-responsiveness or reversible airflow obstruction for up to 28 days, 67% were eosinophilic, 31% paucigranulocytic, and 2% were mixed. There were no patients with neutrophilic asthma.
Eighty-eight of the patients then completed 28 days or more of treatment with fluticasone 1000 µg. The classification of asthma differed significantly after treatment; with 39% of patients eosinophilic, 46% paucigranulocytic, 3% mixed, and 5% neutrophilic.
The treatment response was significantly greater among EA patients than those with NEA with regard to symptoms, quality of life, airway hyperresponsiveness, and exhaled nitric oxide. However, significant changes also occurred in patients with NEA, such as those with paucigranulocytic asthma.
In the analysis, exhaled nitric oxide was the best predictor of steroid response in NEA.
"While identifying the eosinophilic phenotype is important, it is not definitive for determining the response to steroid therapy," conclude Taylor and colleagues.
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