Excerpt from Bronchiectasis

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Background

Bronchiectasis is defined as localized irreversible dilatation of part of the bronchial tree. Involved bronchi are dilated, inflamed, and easily collapsible, resulting in airflow obstruction and impaired clearance of secretions. Bronchiectasis is associated with a wide range of disorders (see Diseases associated with bronchiectasis in the Pathophysiology section, below), but it usually results from necrotizing bacterial infections, such as infections caused by the Staphylococcus or Klebsiella species or Bordetella pertussis. Diagnosis is based on a clinical history of daily viscid sputum production and characteristic computed tomography (CT) scanning findings (see CT Scan).

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Pathophysiology

By definition, bronchiectasis demonstrates localized, irreversible dilatation of bronchi > 2 mm in diameter that results from destruction of the muscular and elastic components of bronchial walls. Damage to these 2 bronchial wall components is caused by an infectious organism and also by the inflammatory cytokines, nitric oxide, and neutrophilic proteases released by the host's immune response to the organism. Additionally, peribronchial alveolar tissue may be damaged, resulting in diffuse peribronchial fibrosis. The result is abnormal bronchial dilatation with bronchial wall destruction and transmural inflammation. The involved bronchi are not only dilated but also inflamed and easily collapsible, resulting in airflow obstruction and impaired clearance of secretions.

The most important functional finding of altered airway anatomy is severely impaired clearance of secretions from the bronchial tree. This altered airway anatomy causes colonization and infection with pathogenic organisms, contributing to the common purulent expectoration observed in patients who have bronchiectasis. The result is a cycle of bronchial damage, bronchial dilatation, impaired clearance of secretions, recurrent infection, and more bronchial damage.

Diseases associated with bronchiectasis are as follows:

• Infection: Typical organisms include Klebsiella species, Staphylococcus aureus, Mycobacterium tuberculosis, Mycoplasma pneumoniae, nontuberculous mycobacteria, Mycobacterium avium-intracellulare complex, measles, pertussis, influenza, respiratory syncytial virus, herpes simplex virus, and certain types of adenovirus.
• Bronchial obstruction: Obstruction occurs as a result of endobronchial tumors, broncholithiasis, bronchial stenosis resulting from infections, encroachment of hilar lymph nodes, and foreign body aspiration.
• Cystic fibrosis
• Young syndrome
• Primary ciliary dyskinesia
• Allergic bronchopulmonary aspergillosis
• Immunodeficiency states: The most common congenital conditions involve B-lymphocyte functions—specifically, hypogammaglobulinemia. An aggressive form of bronchiectasis has been described in patients with acquired immunodeficiency syndrome (AIDS).
• Congenital anatomic defects
  • Bronchopulmonary sequestration
  • Williams-Campbell syndrome (congenital cartilage deficiency)
  • Mounier-Kuhn syndrome (tracheobronchomegaly)
  • Swyer-James syndrome (unilateral hyperlucent lung)
  • Yellow nail syndrome
• a₁-Antitrypsin deficiency
• Lung and bone marrow transplants
• Rheumatoid arthritis and Sjögren syndrome
• Traction bronchiectasis associated with pulmonary fibrosis

Frequency

United States

The incidence of bronchiectasis declined after the introduction of immunizations (pertussis) and antibiotics. The exact overall incidence is not known because the symptoms are not specific, and minor forms often remain undiagnosed. The prevalence is highest among persons in lower socioeconomic groups.

International

Bronchiectasis is an important cause of morbidity in underdeveloped countries. Its incidence has diminished in developed countries, but it is still an important cause of morbidity, especially in children.

Mortality/Morbidity

• Mortality is related to progressive respiratory failure and cor pulmonale rather than to uncontrolled infection. Hemoptysis is common but rarely causes death.
• Complications include recurrent pneumonia, empyema, pneumothorax, and lung abscess. Amyloidosis and metastatic abscesses, common causes of morbidity and mortality in the preantibiotic era, are now uncommon.

Race

No racial predilection exists. A 4-fold higher incidence occurs in American Indians and in Alaskan Native Americans (Redding et al, 2004).

Sex

No sex predilection exists.

Age

In patients with cystic fibrosis, bronchiectasis usually appears in childhood, but its onset may be delayed to adulthood.

Anatomy

Bronchiectasis usually involves bronchi of medium size (>2 mm diameter). The proximal (main, lower, and segmental) bronchi are less affected, because they contain more cartilage than the distal bronchi and because they are more resistant to dilation. However, in patients with allergic bronchopulmonary aspergillosis and cystic fibrosis, the proximal bronchi are typically involved.

Although bronchiectasis caused by bacterial and viral infections usually affects the lower pulmonary lobes, the upper lobes are more frequently affected in patients with allergic bronchopulmonary aspergillosis and tuberculosis. Bronchiectasis is more diffuse in patients with cystic fibrosis and those with immunodeficiency states.

In advanced cases of bronchiectasis, dilated, medium-sized bronchi extend close to the pleura, without side branches and with few normal surrounding lung parenchyma. Focal destruction of part of the bronchial wall, increased mucus secretion and retention, and peribronchial fibrosis occur; the surrounding lung shows volume loss, fibrosis, emphysema, and nodular inflammatory foci.

In 1950, Reid classified bronchiectasis as cylindrical, cystic, or varicose.

• In cylindrical bronchiectasis, bronchi have a uniform caliber, they do not taper, and they have parallel walls.
• Cystic or saccular bronchiectasis is a severe form of bronchiectasis. The involved bronchi are cystlike in appearance and extend to the pleural surface. Air-fluid levels are commonly present.
• Varicose bronchiectasis is relatively uncommon. The bronchi have a beaded appearance with a dilated bronchus and interspersed sites of relative narrowing.

Clinical Details

History

The classic triad of symptoms (chronic cough, excess purulent sputum production, repeated infections) is seen only in the most severely affected patients. Total daily sputum production has been used to characterize severity of bronchiectasis:

• 10 mL/d is defined as mild bronchiectasis.
• 10-150 mL/d is defined as moderate bronchiectasis.
• 150 mL/d is defined as severe bronchiectasis.

Many patients have only mild or intermittent symptoms. Some patients with mild forms of bronchiectasis, as revealed on high-resolution computed tomography (HRCT) scans, may have no symptoms.

Hemoptysis is common and may occur in as many as 50% of patients (Tsao and Lin, 2002). Episodic hemoptysis with little to no sputum production (dry bronchiectasis) is usually a sequela of tuberculosis. However, massive hemoptysis may occur; bleeding usually originates in dilated bronchial arteries, which contain blood at systemic (rather than pulmonary) pressures.

Less-specific symptoms include dyspnea, pleuritic chest pain, wheezing, fever, weakness, and weight loss. Significant airway obstruction may occur as a result of the bronchitis, bronchiolitis, or emphysema that frequently accompanies bronchiectasis. Repeated bronchial infection and pneumonia are common.

Physical examination

Findings are nonspecific and may be attributed to other conditions. On auscultation, crackles, rhonchi, wheezing, and inspiratory squeaks may be detected. Digital clubbing is reported in 37-51% of patients with bronchiectasis (Edwards et al, 2003). Edwards and colleagues found that children with digital clubbing and chest deformity showed significantly higher scores for the extent of their bronchiectasis, bronchial wall dilatation and thickness, and overall changes based on CT scanning scores. Cyanosis, plethora, wasting, weight loss, nasal polyps, and signs of chronic sinusitis may be present. In patients with advanced disease, signs of cor pulmonale may be detected.

Preferred Examination

Chest radiography is usually the first imaging examination, but the findings are often nonspecific and the images may appear normal. HRCT scanning has become the imaging modality of choice for demonstrating or ruling out bronchiectasis and its extent (see Image 2, Image 4, Image 7, Images 10-12). HRCT scanning also helps clinicians evaluate the status of the surrounding lung tissue and exclude other lesions such as neoplasms.

Bronchography was the classic modality used and, until the advent of HRCT scanning, was the only imaging method to demonstrate bronchiectasis. Bronchography is performed by instilling an iodine-based contrast material via a catheter or bronchoscope, but it is rarely, if ever, performed today, as HRCT scanning has replaced it as the diagnostic modality of choice. HRCT scanning is noninvasive and has a sensitivity of 96% and a specificity of 93% (Hansell, 1998).

Laboratory testing may be helpful:

• Results of sputum culture and analysis may reinforce the diagnosis of bronchiectasis and add significant information regarding potential etiologies.
• Complete blood counts are often abnormal in patients who have bronchiectasis.
• Quantitative immunoglobulin (Ig) levels, including levels of the IgG subclasses, IgM, and IgA, are used to exclude hypogammaglobulinemia.
• Quantitative a₁-antitrypsin levels are used to exclude deficiency.
• Pilocarpine iontophoresis (sweat testing) is used to detect cystic fibrosis.
• Pulmonary function test results may be normal or abnormal but can be useful in making a functional assessment of the patient. The most common abnormality is an obstructive airway defect.

Bronchoscopy is not helpful in diagnosing bronchiectasis, but it may be used to identify underlying abnormalities, such as tumors and foreign bodies.

Limitations of Techniques

Chest radiographs may be negative in patients with minor to moderate disease. Many abnormal radiographic findings may be nonspecific, and confirmation using HRCT scanning may be required (see Radiograph).

Bronchography is rarely indicated (see Radiograph) because it is invasive and is associated with allergic reactions to the contrast material. Bronchography also carries the risk of acute bronchoconstriction.

HRCT scanning is the diagnostic modality of choice and has few limitations (see CT Scan).

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