Plastic bronchitis (PB) is a rare and serious respiratory condition characterized by the formation of solid, branching plugs—known as bronchial casts—within the airways. These casts are molds of the bronchial tree, and their presence causes significant obstruction, leading to severe respiratory distress. The term “plastic” refers to the rubbery, cohesive consistency of these casts, distinguishing them from typical mucus plugs. Prompt medical identification and intervention are necessary because this condition can quickly lead to life-threatening airway blockage.
The Nature of Plastic Bronchitis
Plastic bronchitis is defined by the physical presence of these firm, three-dimensional casts that perfectly mimic the shape of the bronchi they occupy. These structures are not simply thick mucus; they possess a cohesive, often rubbery texture allowing them to be expectorated whole or removed intact during a procedure. The composition of the casts is varied, but generally consists of a mix of proteins, fibrin, inflammatory cells, and mucus.
Experts often categorize the casts into two main groups based on their composition and associated underlying condition. Type I casts are inflammatory, composed primarily of fibrin and inflammatory cells, often seen in conditions like severe asthma. Type II casts are non-inflammatory, acellular, and rich in proteinaceous lymph or chylous material, most commonly associated with congenital heart disease and lymphatic abnormalities. The formation process involves the leakage of this protein-rich fluid into the airways, where it coagulates upon exposure to air and forms the occlusive plug.
Underlying Causes and Risk Factors
Plastic bronchitis is almost always a secondary manifestation of an underlying medical condition, not a disease that arises on its own. The most common cause is related to congenital heart disease, specifically in patients who have undergone the Fontan procedure. This palliative surgery, performed for complex single-ventricle defects, creates a circulation where blood flows directly to the lungs without a pumping ventricle.
The Fontan circulation results in abnormally high central venous pressure, which strains the lymphatic system and leads to a lymphatic flow disorder. This pressure causes protein-rich lymph fluid to leak from peribronchial lymphatic channels directly into the airways, forming the Type II casts. Approximately 4–14% of patients who undergo the Fontan procedure will develop plastic bronchitis as a complication. Other associations include chronic inflammatory conditions like severe asthma, cystic fibrosis, and sickle cell disease, which tend to produce the inflammatory Type I casts.
Clinical Presentation and Diagnosis
The symptoms of plastic bronchitis are related to the airway obstruction caused by the casts. Patients typically present with severe respiratory distress, a persistent, forceful cough, and wheezing that may be localized to one area of the lung. The hallmark sign is the expectoration of the branching, tree-like bronchial casts.
The casts can be quite large, sometimes molding the entire bronchial tree of a lung segment, and coughing them up can be frightening and painful. Clinicians initiate diagnosis with non-invasive imaging, such as a chest X-ray or CT scan, which may reveal atelectasis or a collapsed lung segment distal to the obstruction. The definitive diagnostic step involves a bronchoscopy, where a flexible or rigid tube is inserted into the airway to directly visualize the cast and confirm its characteristic appearance. Advanced imaging techniques, like dynamic contrast-enhanced magnetic resonance lymphangiography (DCMRL), are increasingly used to map the abnormal lymphatic flow responsible for cast formation in Fontan-associated cases.
Treatment Strategies
Treatment for plastic bronchitis focuses on two immediate goals: removing the existing casts to maintain an open airway and preventing the formation of new casts. The acute intervention involves removing the obstructing material, most often accomplished through flexible or rigid bronchoscopy. During this procedure, specialized tools are used to extract the cohesive, rubbery plugs, which rapidly improve the patient’s breathing status.
Pharmacological treatments are employed to help dissolve the casts or prevent their formation. Nebulized mucolytics, such as N-acetylcysteine, are used to thin the mucus component, making the casts easier to cough up or remove. In cases where the casts are primarily fibrinous, the fibrinolytic agent tissue plasminogen activator (tPA) is sometimes administered directly into the airways via nebulization to break down the clot structure.
Long-term management requires addressing the underlying cause, which is particularly complex in patients with lymphatic plastic bronchitis. Minimally invasive procedures like lymphatic embolization can be performed to identify and seal the leaking lymphatic channels, effectively stopping the source of the cast material. In the most severe cases of Fontan failure, a heart transplant may be considered, as it resolves the underlying high central venous pressure and lymphatic dysfunction.