Endobronchial biopsy in the final diagnosis of chronic obstructive pulmonary disease and asthma: a clinicopathological study

BACKGROUND: Asthma and chronic obstructive pulmonary disease (COPD) are chronic conditions with an increasing prevalence in developing countries. The evaluation of endobronchial biopsies has emerged as a tool to differentiate between both conditions via the measurement of the reticular basement membrane (RBM) thickness with various conclusions drawn from different studies. OBJECTIVES: Compare the thickness of the RBM between asthma and COPD and evaluate other histomorphological features in both groups. DESIGN: Prospective, descriptive and analytical. SETTING: University teaching hospital. PATIENTS AND METHODS: The study included patients with COPD and irreversible and reversible asthma with diagnosis based on clinical assessment, pulmonary function tests and high-resolution computed tomography scans. Endobronchial biopsies were obtained from all patients and, using a light microscope and a computerized image analyzer, the thickness of the reticular basement membrane was calculated in all patients. We also made a qualitative assessment of other histomorphological features. MAIN OUTCOME MEASURES: Mean RBM thickness. SAMPLE SIZE: Thirty male patients. RESULTS: The mean RBM thickness in asthmatic patients was 8.9 (2.4) μm. The mean RBM thickness in COPD patients was 5.3 (1.1) μm. However, there was no thickening of the RBM in patients with reversible asthma. The RBM was significantly thicker in patients with irreversible asthma than in patients with COPD or reversible asthma. There were no significant differences in epithelial desquamation or metaplasia, mucosal or submucosal inflammation, the presence of eosinophils, submucosal glandular hyperplasia or submucosal smooth muscle hyperplasia between groups. CONCLUSIONS: The thickness of the RBM is the only reproducible histopathological feature to differentiate COPD from irreversible asthma. LIMITATIONS: The study included a limited number of patients. A qualitative approach was used to compare epithelial cell injury, inflammation, submucosal glandular and muscular hyperplasia.