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Plastic Bronchitis


Plastic bronchitis is a rare condition characterized by recurrent episodes of airway obstruction secondary to the formation of large proteinaceous branching casts that take on the shape of and obstruct the tracheobronchial tree. It is not a single disease entity, but rather represents a state of altered respiratory epithelial function and is most frequently encountered in the setting of underlying pulmonary or cardiac disease, although plastic bronchitis may also arise in lymphatic disorders, pulmonary infections, and the acute chest syndrome of sickle cell disease ( Table 419.1 ). In comparison with the smaller bronchial and bronchiolar casts seen with mucus plugging, the lesions of plastic bronchitis are more extensive, with casts that can outline large segments of the airway to the level of the terminal bronchioles ( Fig. 419.1 ). These casts may be spontaneously expectorated or may require bronchoscopic removal for relief of potentially fatal airway obstruction. Cast composition varies, although it typically consists of either a fibrin-predominant or mucin-predominant laminated matrix with or without inflammatory cell infiltration. Plastic bronchitis may be classified according to an associated disease, the cast histology, or a combination.

Table 419.1
Conditions Associated With Plastic Bronchitis
From Rubin BK: Plastic bronchitis, Clin Chest Med 37:405–408, 2016 (Box 1, p. 406).
PROVEN CONDITIONS

  • Congenital heart disease with Fontan physiology

  • Pulmonary lymphatic anomalies

  • Influenza A pulmonary infection

POSSIBLE CONDITIONS

  • Toxic inhalation

  • Sickle cell acute chest syndrome

  • Hypersecretory and near-fatal asthma (eosinophilic casts)

UNLIKELY AND UNPROVEN CONDITIONS

  • Cystic fibrosis

  • Chronic obstructive pulmonary disease

  • Bronchiectasis

  • Bacterial pneumonia

Fig. 419.1
Tracheobronchial casts following bronchoscopic extraction. Casts show branched architecture corresponding to the bronchial tree.

(From Corrin B, Nicholson AG: Pathology of the lungs , ed 3, London, 2011, Churchill Livingstone. Fig 3.20.)

Epidemiology

Plastic bronchitis is rare, and its true prevalence in the pediatric population is not known but is estimated to be 6.8 cases per 100,000 patients. Prevalence does vary in relation to the underlying associated disease state, with rates as high as 4–14% estimated in patients who have undergone staged palliation of complex congenital heart disease and much lower rates seen complicating asthma and atopic disease. A slight male predominance exists for cast formation in the setting of structural heart disease, whereas cast formation in the setting of asthma and atopic disease demonstrates a female predominance. Children with single-ventricle Fontan physiology are at high risk for developing plastic bronchitis.

Pathogenesis

The mechanism of cast formation is unclear, although it is believed to vary based on the underlying disease association and cast type. One classification system differentiates type 1 inflammatory casts, composed primarily of fibrin with neutrophilic or more often eosinophilic infiltration, and type 2 acellular casts, composed primarily of mucin with little to no cellular infiltration. Type 1 casts tend to be associated with inflammatory and infectious disorders of the lung, whereas type 2 casts tend to be associated with surgically palliated structural heart disease, particularly single ventricle lesions. However, these distinctions are not absolute; patients with structural heart disease can have fibrin-predominant casts, and patients with asthma or atopic disease can have mucin-predominant casts, with both mucin casts and fibrin casts demonstrating various degrees of cellular infiltration.

Cast formation in the setting of structural heart disease may result from alterations in pulmonary blood flow or lymphatic drainage, particularly following staged surgical palliation. Under these circumstances, increased central venous pressure is believed to compromise the integrity of the bronchial mucosa, impeding lymphatic flow and resulting in the development of collateral lymphatic vessels and potentially of lymphoalveolar fistulae that may exude proteinaceous material into the airway lumen.

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