Bronchiectasis : Causes, Etiology, Pathogenesis, Symptoms, Diagnosis, Treatment, Prognosis & Prevention
Definition
- Bronchiectasis refers to an irreversible airway dilation that involves the lung in either a focal or a diffuse manner.
- It classically has been categorized as cylindrical or tubular (the most common form), varicose, or cystic.
Etiology
Bronchiectasis can arise from infectious or noninfectious causes. Clues to the underlying etiology are often provided by the pattern of lung involvement.
- Focal bronchiectasis refers to bronchiectatic changes in a localized area of the lung and can be a consequence of obstruction of the airway—either extrinsic (e.g., due to compression by adjacent lymphadenopathy or parenchymal tumor mass) or intrinsic (e.g., due to an airway tumor or aspirated foreign body, a scarred/stenotic airway, or bronchial atresia from congenital underdevelopment of the airway).
- Diffuse bronchiectasis is characterized by widespread bronchiectatic changes throughout the lung and
often arises from an underlying systemic or infectious disease process. More pronounced involvement of the upper lung fields is most common in cystic fibrosis (CF) and is also observed in postradiation fibrosis, corresponding to the lung region encompassed by the radiation port. - Bronchiectasis with predominant involvement of the lower lung fields usually has its source in chronic recurrent aspiration (e.g., due to esophageal motility disorders like those in scleroderma), endstage fibrotic lung disease (e.g., traction bronchiectasis from idiopathic pulmonary fibrosis), or recurrent immunodeficiency-associated infections (e.g., hypogammaglobulinemia).
- Bronchiectasis resulting from infection by nontuberculous mycobacteria (NTM), most commonly the Mycobacterium avium-intracellulare complex (MAC), often preferentially affects the midlung fields. Congenital causes of bronchiectasis with predominant midlung field involvement include the dyskinetic/ immotile cilia syndrome. Finally, predominant involvement of the central airways is reported in association with allergic bronchopulmonary aspergillosis (ABPA), in which an immune-mediated reaction to Aspergillus damages the bronchial wall. Congenital causes of central airway–predominant bronchiectasis resulting from cartilage deficiency include tracheobronchomegaly (Mounier-Kuhn syndrome) and Williams-Campbell syndrome.
- In many cases, the etiology of bronchiectasis is not determined. In case series, as many as 25–50% of patients referred for bronchiectasis have idiopathic disease.
Epidemiology
- The overall reported prevalence of bronchiectasis in the United States has recently increased, but the epidemiology of bronchiectasis varies greatly with the underlying etiology.
- In general, the incidence of bronchiectasis increases with age.
- Bronchiectasis is more common among women than among men.
- In areas where tuberculosis is prevalent, bronchiectasis more frequently occurs as a sequela of granulomatous infection.
- Focal bronchiectasis can arise from extrinsic compression of the airway by enlarged granulomatous lymph nodes and/or from development of intrinsic obstruction as a result of erosion of a calcified lymph node through the airway wall (e.g., broncholithiasis).
- Especially in reactivated tuberculosis, parenchymal destruction from infection can result in areas of more diffuse bronchiectasis.
- Apart from cases associated with tuberculosis, an increased incidence of non-CF bronchiectasis with an unclear underlying mechanism has been reported as a significant problem in developing nations.
- It has been suggested that the high incidence of malnutrition in certain areas may predispose to immune dysfunction and development of bronchiectasis.
Pathogenesis
The most widely cited mechanism of infectious bronchiectasis is the “vicious cycle hypothesis,” in which susceptibility to infection and poor mucociliary clearance result in microbial colonization of the bronchial tree.
Some organisms, such as Pseudomonas aeruginosa, exhibit a particular propensity for colonizing damaged airways and evading host defense mechanisms.
Proposed mechanisms for noninfectious bronchiectasis include immune-mediated reactions that damage the bronchial wall (e.g., those associated with systemic autoimmune conditions such as Sjögren’s syndrome and rheumatoid arthritis).
Traction bronchiectasis refers to dilated airways arising from parenchymal distortion as a result of lung fibrosis (e.g., postradiation fibrosis or idiopathic pulmonary fibrosis).
Clinical Symptoms
- The most common clinical presentation is a persistent productive cough with ongoing production of thick, tenacious sputum.
- Physical findings often include crackles and wheezing on lung auscultation, and some patients with bronchiectasis exhibit clubbing of the digits.
- Mild to moderate airflow obstruction is often detected on pulmonary function tests, overlapping with that seen at presentation with other conditions, such as chronic obstructive pulmonary disease (COPD).
Acute exacerbations of bronchiectasis are usually characterized by changes in the nature of sputum production, with increased volume and purulence. However, typical signs and symptoms of lung infection, such as fever and new infiltrates, may not be present.
Diagnosis
Diagnosis is based on Clinical menifestation, Radiographs, Chest computed tomography (CT) and a workup to determine the underlying etiology. Evaluation of focal bronchiectasis almost always requires bronchoscopy to exclude airway obstruction by an underlying mass or foreign body. A workup for diffuse bronchiectasis includes analysis for the major etiologies, with an initial focus on excluding CF. Pulmonary function testing is an important component of a functional assessment of the patient.
Radiographs
- The diagnosis is usually based on presentation with a persistent chronic cough and sputum production accompanied by consistent radiographic features.
- Although chest radiographs lack sensitivity, the presence of “tram tracks” indicating dilated airways is consistent with bronchiectasis.
Chest computed tomography (CT)
- Chest computed tomography (CT) is more specific for bronchiectasis and is the imaging modality of choice for confirming the diagnosis.
- CT findings include airway dilation (detected as parallel “tram tracks” or as the “signet-ring sign”—a cross-sectional area of the airway with a diameter at least 1.5 times that of the adjacent vessel), lack of bronchial tapering (including the presence of tubular structures within 1 cm from the pleural surface), bronchial wall thickening in dilated airways, inspissated secretions (e.g., the “tree-in-bud” pattern), or cysts emanating from the bronchial wall (especially pronounced in cystic bronchiectasis).
Treatment
Treatment of infectious bronchiectasis is directed at the control of active infection and improvements in secretion clearance and bronchial hygiene so as to decrease the microbial load within the airways and minimize the risk of repeated infections.
Antibiotic Treatment
- Antibiotics targeting the causative or presumptive pathogen (with Haemophilus influenzae and P. aeruginosa isolated commonly) should be administered in acute exacerbations, usually for a minimum of 7–10 days and perhaps for as long as 14 days.
- Decisions about treatment of NTM infection can be difficult, given that these organisms can be colonizers as well as pathogens and the prolonged treatment course often is not well tolerated. MAC strains are the most common NTM pathogens, and the recommended regimen for HIV-negative patients includes a macrolide combined with rifampin and ethambutol.
Bronchial Hygiene
- The numerous approaches used to enhance secretion clearance in bronchiectasis include hydration and mucolytic administration, aerosolization of bronchodilators and hyperosmolar agents (e.g., hypertonic saline), and chest physiotherapy (e.g., postural drainage, traditional mechanical chest percussion via hand clapping to the chest, or use of devices such as an oscillatory positive expiratory pressure flutter valve or a high-frequency chest wall oscillation vest).
- Pulmonary rehabilitation and a regular exercise program may assist with secretion clearance as well as with other aspects of bronchiectasis, including improved exercise capacity and quality of life.
- The mucolytic dornase (DNase) is recommended routinely in CF-related bronchiectasis but not in non-CF bronchiectasis, given concerns about lack of efficacy and potential harm in the non-CF population.
Anti-inflammatory Therapy
- It has been proposed that control of the inflammatory response may be of benefit in bronchiectasis. However, no significant differences in lung function or bronchiectasis exacerbation rates have been observed. Risks of immunosuppression and adrenal suppression must be carefully considered with use of anti-inflammatory therapy in infectious bronchiectasis.
- Nevertheless, administration of oral/systemic glucocorticoids may be important in treatment of bronchiectasis due to certain etiologies, such as ABPA, or of noninfectious bronchiectasis due to underlying conditions, especially that in which an autoimmune condition is believed to be active (e.g., rheumatoid arthritis or Sjögren’s syndrome).
- Patients with ABPA may also benefit from a prolonged course of treatment with the oral antifungal agent itraconazole.
Refractory Cases : In select cases, surgery can be considered, with resection of a focal area of suppuration. In advanced cases, lung transplantation can be considered.
Complications
- In more severe cases of infectious bronchiectasis, recurrent infections and repeated courses of antibiotics can lead to microbial resistance to antibiotics.
- In certain cases, combinations of antibiotics that have their own independent toxicity profiles may be necessary to treat resistant organisms.
- Recurrent infections can result in injury to superficial mucosal vessels, with bleeding and, in severe cases, life-threatening hemoptysis.
- Management of massive hemoptysis usually requires intubation to stabilize the patient, identification of the source of bleeding, and protection of the nonbleeding lung. Control of bleeding often necessitates bronchial artery embolization and, in severe cases, surgery.
Prognosis
- Outcomes of bronchiectasis can vary widely with the underlying etiology and may also be influenced by the frequency of exacerbations and (in infectious cases) the specific pathogens involved.
Prevention
- Reversal of an underlying immunodeficient state (e.g., by administration of gamma globulin for immunoglobulin-deficient patients) and vaccination of patients with chronic respiratory conditions (e.g., influenza and pneumococcal vaccines) can decrease the risk of recurrent infections.
- Patients who smoke should be counseled about smoking cessation.
After resolution of an acute infection in patients with recurrences (e.g., ≥3 episodes per year), the use of suppressive antibiotics to minimize the microbial load and reduce the frequency of exacerbations has been proposed, although there is less consensus with regard to this approach in non-CF-associated bronchiectasis than in patients with CF-related bronchiectasis. Possible suppressive treatments include
- Administration of an oral antibiotic (e.g., ciprofloxacin) daily for 1–2 weeks per month;
- Use of a rotating schedule of oral antibiotics (to minimize the risk of development of drug resistance);
- Administration of a macrolide antibiotic daily or three times per week (with mechanisms of possible benefit related to non-antimicrobial properties, such as anti-inflammatory effects and reduction of gramnegative bacillary biofilms);
- Inhalation of aerosolized antibiotics (e.g., tobramycin inhalation solution) by select patients on a rotating
schedule (e.g., 30 days on, 30 days off ), with the goal of decreasing the microbial load without eliciting the side effects of systemic drug administration; - Intermittent administration of IV antibiotics (e.g., “clean-outs”) for patients with more severe bronchiectasis
and/or resistant pathogens.
