To the Editor:
Chronic obstructive pulmonary disease (COPD) is a heterogeneous condition, with patients displaying varying clinical and pathophysiological features. The identification of COPD phenotypes with distinct characteristics may allow targeted treatment strategies directed towards specific biological pathways.
Eosinophilic inflammation is thought to be a characteristic feature of asthma rather than COPD. However, studies have shown that a subset of COPD patients with eosinophilic airway inflammation exists, even after the careful exclusion of patients with any features of asthma, such as β-agonist reversibility, bronchial hyperresponsiveness, atopy or a childhood history of asthma [1–4]. Interestingly, these patients exhibit the greatest response to corticosteroid treatment [1–4]. Likewise, sputum eosinophil numbers are increased in a subset of COPD exacerbations [5, 6], and titrating corticosteroid therapy according to sputum eosinophil counts reduces exacerbation rates [7]. Furthermore, there are similar increases in sputum and blood eosinophil numbers during COPD exacerbations [5]; using blood eosinophils as a surrogate maker for airway eosinophils to direct oral corticosteroid therapy for the treatment of COPD exacerbations enhances clinical recovery [8]. Taken together, these observations suggest that eosinophilic airway inflammation in COPD is a predictive biomarker of corticosteroid responsiveness during clinical stability and exacerbations.
The prevalence of eosinophilic inflammation in COPD patients is unknown. We do not know whether patients with sputum or blood eosinophilia represent a stable COPD phenotype over time and, apart from corticosteroid responsiveness, little is known about the other clinical characteristics of this subset of patients.
We analysed samples from the ECLIPSE (Evaluation of COPD Longitudinally to Identify …
