Chapter 51: Bronchiectasis

INTRODUCTION

Bronchiectasis is an entity characterized pathologically by airway inflammation, and permanent bronchial dilatation, and clinically by cough, sputum production, and exacerbations with recurrent respiratory tract infections. Bronchiectasis has a long history, having been first described formally by Laennec in the early 19th century.

Bronchiectasis is a heterogeneous syndrome with many different contributing etiologies. No animal model exists for bronchiectasis, and its pathogenesis remains poorly understood. It is a disease characterized by airway inflammation arising from infection in genetically susceptible individuals. Permanent damage to ciliated airway epithelium usually results from direct impact of bacterial pathogens (neutrophil recruitment via glycoproteins and IL-8, biofilm formation), as well as neutrophil-mediated host response to these pathogens. This results in direct damage to bronchial walls, epithelial cell damage, and goblet cell hyperplasia. Human neutrophil elastase (HNE), a proteolytic enzyme mainly involved in the response against bacteria, is thought to play a key role in producing tissue damage. Peter Cole described a “vicious circle” hypothesis that provides a useful conceptual framework: According to the hypothesis, neutrophilic inflammation caused by an initial insult results in airway destruction in susceptible individuals. The anatomic disruption leads to abnormal mucus clearance, setting the stage for chronic bacterial infection that then propagates the cycle of airway inflammation and bronchiectasis.¹

Although it has been described as an orphan disease, bronchiectasis unrelated to cystic fibrosis (CF) is commonly recognized in clinical practice. Based on a large, geographically diverse health insurance claims database, the prevalence of non-CF bronchiectasis has been estimated at 52 cases/100,000, with an estimated total number of total cases greater than 110,000 in the United States.² A more recent study suggested a higher prevalence of 139 cases per 100,000 persons.³

The prevalence of bronchiectasis increases with age and appears to be more common in women (1.3- to 1.6-fold higher prevalence) and Asians (2.5- and 3.9-fold higher prevalence in Caucasians and African Americans, respectively). The prevalence has increased by 8.7% per year.⁴ Similar epidemiologic findings have been reported in Europe; the incidence and point prevalence of bronchiectasis increased yearly during the period between 2004 and 2013.⁵

Bronchiectasis is also associated with significant economic cost, including that associated with an increased number of hospitalizations compared with age-matched controls. Finally, bronchiectasis is associated with a notable impairment of quality of life and mortality, likely influenced by sputum volume, severity of airflow obstruction, and the presence of chronic gram-negative infection, particularly with Pseudomonas aeruginosa.

DIAGNOSIS

Establishing a diagnosis of bronchiectasis requires an organized and systematic approach, with consideration of the elements of the history and physical examination, chest imaging, and laboratory data, as well as additional studies. Identifying specific underlying causes of bronchiectasis is equally important, as doing so may directly impact treatment in as many as 40% of patients.⁶

Clinical Presentation

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