Eosinophilic airway inflammation is a main feature of unstable asthma in adolescents
Stability of asthma is based not only on the long-term control of symptoms and exacerbations, but also on clinical phenotype. ICS are widely used for long-term control of asthma and previous research has established an association between a patient’s response to ICS and their cytological inflammatory phenotype. Eosinophilic inflammatory asthma, for example, is relatively resistant to high-dose ICS. In mild asthma, management of symptoms using ICS is usually sufficient to achieve stable asthma, but ICS alone is not sufficient for moderate and severe asthma. This cross-sectional study aimed to characterise the inflammatory profile of stable and unstable asthma in adolescents treated with moderate- and high-dose ICS.
The study participants were children and adolescents (N=139, mean age = 16.8 years) with active asthma, who were non-smokers receiving treatment with moderate- to high-dose ICS for at least one year. Between January 2012 and February 2014, participants completed a three-month observation period, during which patients recorded their symptoms and medication use and completed a number of diagnostic and observational tests. Of 139 participants, 72 were classified as having stable asthma and 67 as having unstable asthma. Clinical and spirometric measurements in both groups were compared, as well as inflammatory markers including fractional exhaled nitric oxide, sputum cytology and bronchial hyperresponsiveness following provocation with hypertonic saline and exercise.
The study found that patients with unstable asthma had more eosinophilic inflammation, bronchial hyperresponsiveness and lower spirometry parameters compared with the stable asthma group. Elevated percentages of eosinophils in induced sputum were seen in the sputum of 75% of patients in the unstable group and a multivariate analysis found that the eosinophil count was significantly associated with asthma instability.
The study relied on self-reporting for medication compliance, a subjective method and limitation of the study, although this approach has been previously used in similar studies. The authors also only performed one sputum eosinophil count, which may not be reflective of the patient’s long-term asthma stability.
In summary, the authors concluded that eosinophilic inflammation is the dominant type of inflammation in unstable asthma. Elevated bronchial hyperresponsiveness and lower spirometric parameters were also associated with asthma instability, which highlights the usefulness of determining the inflammatory phenotype of unstable asthma patients.