We read with interest the study by Park et al1 published recently in Thorax. We agree that non‐asthmatic eosinophilic bronchitis (EB), a condition characterised by eosinophilic inflammation without evidence of variable airflow obstruction, is a powerful disease control group to study the mechanisms involved in the development of airway hyperresponsiveness in asthma. Previous comparative studies have shown that asthma and EB are immunopathologically similar but that there are key differences—namely, mast cell localisation to the airway smooth muscle bundle2 and increased IL‐13 expression in asthma. Park et al1 have proposed in their recent study that this list needs to be extended to include increased airway wall area as a feature confined to asthma. This is an important observation as other HRCT studies in asthma have suggested that increased airway wall area may, in fact, protect against airway hyperresponsiveness.3 However, the observed absence of increased airway wall area in the EB group studied may not reflect distinct differences between this disease and asthma, but may simply reflect duration of disease.
The subjects with EB had participated in an earlier study.4 In this study duration of disease was on average about 7 months and very few subjects had symptoms or evidence of inflammation for more than 1 year. The duration of disease in the asthma group is not clear from the current study, but this is likely to be years in many cases. This point needs to be clarified as conclusions made about possible differences in remodelling between asthma and EB are undermined if the disease duration is markedly different.
In our experience, some patients with EB and prolonged eosinophilic airway inflammation have a progressive decline in their lung function,5 suggesting that airway wall remodelling is a feature in some patients with this condition. Whether airway remodelling and increased airway wall thickness are features shared by asthma and EB or are specific to the asthma phenotype therefore remains to be fully addressed.
Footnotes
Competing interests: none declared.
References
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