Bronchial dilatation in asthma: relation to clinical and sputum indices

Investigations using high-resolution CT (HRCT) show that bronchial dilatation (BD) is found in many patients with asthma. However, the pathogenesis and pathophysiologic relevance of BD in asthma are poorly understood. A balance between matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) may control the remodeling of extracellular matrix, and excess MMPs have been associated with destruction or dilatation of airways in patients with bronchiectasis.

To study the prevalence of BD as assessed by HRCT according to standard subjective criteria in 37 patients with stable asthma and 10 healthy control subjects, and to examine the relation of BD in asthmatic patients to clinical characteristics and sputum indices, including MMP-9 and TIMP-1 levels.

A prospective cohort study.

At least one dilated bronchus was present in 23 asthmatic subjects (62%) and 2 control subjects (20%) [p = 0.030]. The ratio of dilated bronchi to all eligible bronchi in each subject (individual BD%) was higher in the asthmatic patients than in the control subjects (11.4 +/- 16.1% vs 1.3 +/- 3.0%, p = 0.011) [mean +/- SD]. Asthmatic patients with (n = 23) and those without BD (n = 14) were similar with regard to age, duration and severity of asthma, atopy, pulmonary function, sputum eosinophil or neutrophil count, and sputum levels of MMP-9 or TIMP-1 and their molar ratio. Individual BD% of asthmatic patients was also unrelated to these clinical and sputum variables. When analysis was confined to the 23 patients with BD, however, individual BD% correlated with the severity score of asthma (r = 0.49, p = 0.023). The results of follow-up HRCT obtained from 19 patients suggested that BD was a fixed rather than transient phenomenon.

BD is more prevalent in asthmatic patients than in normal subjects and might be associated with the severity of asthma. Cellular inflammation or possible imbalance between MMP-9 and TIMP-1 was not demonstrated in this study to be related to BD in asthma.