Bronchiectasis refers to an irreversible airway dilation that involves the lung in either a focal or a diffuse manner and that classically has been categorized as cylindrical or tubular (the most common form), varicose, or cystic.
Bronchiectasis can arise from infectious or noninfectious causes (Table 258-1). 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.
Table 258-1 Major Etiologies of Bronchiectasis and Proposed Workup
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Table 258-1 Major Etiologies of Bronchiectasis and Proposed Workup
|Pattern of Lung Involvement by Bronchiectasis||Etiology by Categories (with Specific Examples)||Workup|
|Focal||Obstruction (e.g., aspirated foreign body, tumor mass)||Chest imaging (chest x-ray and/or chest CT); bronchoscopy|
|Diffuse||Infection (e.g., bacterial, nontuberculous mycobacterial)||Gram's stain/culture; stains/cultures for acid-fast bacilli and fungi. If no pathogen is identified, consider bronchoscopy with bronchoalveolar lavage (BAL)|
|Immunodeficiency (e.g., hypogammaglobulinemia, HIV infection, bronchiolitis obliterans after lung transplantation)||Complete blood count with differential; immunoglobulin measurement; HIV testing|
|Genetic causes (e.g., cystic fibrosis, Kartagener's syndrome, α1 antitrypsin deficiency)||Measurement of chloride levels in sweat (for cystic fibrosis), α1 antitrypsin levels; nasal or respiratory tract brush/biopsy (for dyskinetic/immotile cilia syndrome); genetic testing|
|Autoimmune or rheumatologic causes (e.g., rheumatoid arthritis, Sjögren's syndrome, inflammatory bowel disease); immune-mediated disease (e.g., allergic bronchopulmonary aspergillosis)||Clinical examination with careful joint exam, serologic testing (e.g., for rheumatoid factor). Consider workup for allergic bronchopulmonary aspergillosis, especially in patients with refractory asthmaa|
|Recurrent aspiration||Test of swallowing function and general neuromuscular strength|
|Miscellaneous (e.g., yellow nail syndrome; traction bronchiectasis from postradiation fibrosis or idiopathic pulmonary fibrosis)||Guided by clinical condition|
|Idiopathic||Exclusion of other causes|
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), end-stage 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.
The epidemiology of bronchiectasis varies greatly with the underlying etiology. For example, patients born with CF often develop significant clinical bronchiectasis in late adolescence or early adulthood, although atypical presentations of CF in adults in their thirties and forties are also possible. In contrast, bronchiectasis resulting from MAC infection classically affects nonsmoking women older than age 50 years. 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 and Pathology
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. Impaired mucociliary clearance can result from inherited conditions such as CF or dyskinetic cilia syndrome, and it has been proposed that a single severe infection (e.g., pneumonia caused by Bordetella pertussis or Mycoplasma pneumoniae) can result in significant airway damage and poor secretion clearance. The presence of the microbes incites continued chronic inflammation, with consequent damage to the airway wall, continued impairment of secretion and microbial clearance, and ongoing propagation of the infectious/inflammatory cycle. Moreover, it has been proposed that mediators released directly from bacteria can interfere with mucociliary clearance.
Classic studies of the pathology of bronchiectasis from the 1950s demonstrated significant small-airway wall inflammation and larger-airway wall destruction as well as dilation, with loss of elastin, smooth muscle, and cartilage. It has been proposed that inflammatory cells in the small airways release proteases and other mediators, such as reactive oxygen species and proinflammatory cytokines, that damage the larger-airway walls. Furthermore, the ...