Significance of emphysema observed on computed tomography scan in asthma

Abstract

Computed tomography (CT) scan has been used in the diagnosis of airways diseases [1] because of the high degree of anatomical detail provided. Most abnormalities, such as bronchiectasis and emphysema, seen on a CT scan have been anatomically validated, but their clinical significance is not always fully understood. Highresolution CT (HR-CT) has been used to study asthmatics [2‐8]. It has been consistently observed that more abnormalities related to fixed airways remodelling, such as bronchial dilatation and bronchiectasis are observed in asthmatic subjects than in normal subjects, although the clinical consequences of these findings are not clear. HRCT scans have also been used to measure the internal size of the airways at baseline, during challenge or after bronchodilatation [9‐12]. However, there is no data on lung density in patients with acute and chronic asthma. This was the aim of the paper published in the present issue of the European Respiratory Journal [13]. The relationship between asthma and emphysema was suggested in 1952 by ROYLE [14] who found emphysema in patients with severe asthma. However, the study was flawed since chest radiographs failed to recognize mild emphysema [15] and most of the patients studied were current or exsmokers. Importance of CT scan in the diagnosis of emphysema Pulmonary emphysema is a pathological diagnosis, but correlations between results of lung function tests and the extent of emphysema are poor. Lung function tests are also nonspecific for emphysema, and alteration of transfer factor of the lung for carbon monoxide (TL,CO) may be due to cardiogenic oedema or interstitial disease. The diagnosis of pulmonary emphysema can be made with relative confidence on the basis of clinical and radiological criteria. Despite the fact that very mild emphysema goes undetected and the severity of the disease may be underestimated, HR-CT is the most sensitive radiographic method with which to image emphysema and has been shown to be more sensitive than pulmonary function tests or TL,CO [15‐18]. Many studies have demonstrated significant correlations between CT scan data and pathological observations of lungs obtained at autopsy or after surgery for both centrilobular and panacinar emphysema [19‐23]. However, occasionally CT scans give false-positive findings and the criteria used