Giới thiệu
Bronchiectasis is the irreversible dilatation and destruction of the bronchi. It results in airflow obstruction and impaired clearance of secretions. This enhances susceptibility to bronchial infection and increases inflammatory reaction, which causes further lung damage.
Dịch tễ học
Although the predominance of bronchiectasis has not been entirely clear, recent studies around the world show increasing incidence of the disease. Current evidence also suggest that it disproportionately affects women and older individuals. It has been noted that the incidence with age with an 8- to 10-fold difference after the age of 60 years as compared to those younger than 40-50 years of age. In the United States (US), bronchiectasis is known to affect as much as 350,000-500,000 adults.
Studies in Asia point to post-tuberculosis (TB) as the most common underlying cause of bronchiectasis. Based on available surveys, the noted overall prevalence of bronchiectasis is 464 cases per 100,000 people in Korea and 1,200 per 100,000 individuals ages ≥40 years in China.
Sinh lý bệnh
The pathophysiology of bronchiectasis can be likened to a vortex, wherein there are 4 important factors that interact with one another, leading to disease and disease progression . These factors are chronic infection, airway inflammation, impaired mucociliary clearance, and structural lung damage. Each of these factors plays a part in the development, progression of the disease and exacerbation. The first step is an insult, mostly infectious, that damages the airways. This, accompanied by impaired mucociliary clearance causes bacterial colonization, which, in turn, leads to the recruitment of neutrophils, macrophages, and other inflammatory mediators. Chronic inflammation ensues, causing structural damage to airways.
Bronchiectasis_Disease BackgroundNguyên nhân
It must be noted that there are various etiologies that can precipitate or contribute to the development of bronchiectasis.
Primary Infections
Necrotizing infections that are not treated properly or untreated are a common cause of bronchiectasis in developing countries. Typical offending organisms include Klebsiella sp, Staphylococcus aureus, Mycobacterium tuberculosis, Mycoplasma pneumoniae, nontuberculous mycobacteria (eg Mycobacterium avium complex, Mycobacterium intracellulare, Mycobacterium abscessus), measles, pertussis, influenza, herpes simplex and certain types of adenovirus. It must be noted that nontuberculous mycobacteria have the propensity to occur as opportunistic infections in patients with bronchiectasis in patients who are immunocompetent. Patients with chronic Pseudomonas aeruginosa colonization are at higher risk for complications.
Bronchial Obstruction and Recurrent Aspiration
Focal post-obstructive bronchiectasis may occur in endobronchial tumors, broncholithiasis, bronchial stenosis from infections, encroachment of hilar lymph nodes and foreign body aspiration. Recurrent aspiration caused by gastroesophageal reflux disease (GERD) or dysphagia may be the cause of bronchiectasis in 1-11.3% of adult patients. Additionally, in adults, foreign body aspiration may occur with altered mental status and when food is not chewed.
Cystic Fibrosis (CF)
Notably, CF is rare in non-white races. It is an autosomal recessive multisystem disorder affecting the chloride transport system in exocrine tissues. Bronchiectasis is the major pulmonary finding of this disease, occurring secondary to mucous-plugged proximal airways and chronic respiratory infection.
Primary Ciliary Dyskinesia
Primary ciliary dyskinesia is rare but can cause poor mucociliary clearance, recurrent respiratory infections and bronchiectasis. Kartagener’s syndrome is characterized by situs inversus, bronchiectasis, chronic sinusitis with immotile cilia.
Allergic Bronchopulmonary Aspergillosis (ABPA)
ABPA is a hypersensitivity reaction to inhaled Aspergillus antigen characterized by bronchospasm, bronchiectasis, and immunologic evidence of a reaction to Aspergillus sp. In this condition, the bronchiectasis is secondary to airway plugs of viscid secretions containing hyphae of Aspergillus sp. In ABPA, chest computed tomography (CT) scan shows central airway bronchiectasis.
Young Syndrome
Young syndrome is clinically similar to CF. Young syndrome patients have the triad of bronchiectasis, sinusitis and obstructive azoospermia.
Immunodeficiency States
Congenital or acquired immunodeficiency usually present with repeated sinus or pulmonary infections. Bronchiectasis in acquired immunodeficiency syndrome has occurred with or without obvious preceding pulmonary infections
Alpha1-Antitrypsin (A1AT) Deficiency and Rheumatic Diseases
Pathogenesis of bronchiectasis in alpha1-antitrypsin deficiency and rheumatic diseases is unclear and may represent only coincidental findings. Patients with A1AT deficiency make up <1% of the population with bronchiectasis. While individuals whose etiology is connected to rheumatoid arthritis account for only 2-5% of patients with bronchiectasis.
Traction Bronchiectasis
Traction bronchiectasis is characterized by distortion of the airways secondary to distortion of the lung parenchyma from pulmonary fibrosis.
Tracheobronchomalacia and Tracheobronchomegaly
Anatomic defects in the airway may lead to the development of bronchiectasis via deficient clearance of respiratory secretions and recurrent infection.
Asthma, Chronic Obstructive Pulmonary Disease (COPD) and Smoking
An interrelationship between asthma and bronchiectasis is suspected; asthma was also identified as an independent risk factor for bronchiectasis. While a causal relationship between COPD, smoking and bronchiectasis have not yet been established, cigarette smoking, COPD and repeated infections or exacerbations can worsen pulmonary function overtime and may accelerate the progression of bronchiectasis.