Bronchiolitis is an inflammatory condition affecting the bronchioles, the smallest airways in the lungs, measuring less than two millimeters in diameter. While commonly recognized as a temporary viral infection in infants, its presentation in adults is fundamentally different and far more serious. Adult bronchiolitis is a rare, complex, and frequently chronic condition stemming from a systemic reaction or exposure rather than a simple acute infection. This distinction is significant because the adult form often leads to permanent lung damage and progressive airflow obstruction. Understanding the specific causes, symptoms, and management of this disease is important for accurate diagnosis and treatment.
Defining Bronchiolitis in Adults
Bronchiolitis in adults involves damage to the small airways, primarily the membranous and respiratory bronchioles. The pathology is characterized by inflammation, edema, and fibrosis, which narrow or obstruct the tiny passageways. This involves structural remodeling of the airway walls, not merely temporary swelling like common bronchitis. Obstruction occurs either due to scarring and concentric narrowing of the wall or the formation of inflammatory plugs within the airway lumen.
The small airways are vulnerable because they lack the structural support of cartilage. Injury in this region significantly increases airway resistance and causes air trapping within the distal air sacs. Adult bronchiolitis is often a manifestation of an underlying disease process, such as an autoimmune disorder or chronic rejection after a transplant. A precise diagnosis often relies on identifying the specific histopathological pattern of the injury.
Distinct Forms and Underlying Causes
The diverse nature of adult bronchiolitis requires classification based on the specific pathological process affecting the small airways. The two major forms are constrictive and proliferative. A third, geographically specific form is Diffuse Panbronchiolitis.
Constrictive Bronchiolitis
Constrictive Bronchiolitis, also known as Bronchiolitis Obliterans, is the most severe form, characterized by irreversible scarring and concentric fibrosis of the bronchiolar walls. This fibrotic material progressively squeezes the airway shut, causing permanent airflow obstruction unresponsive to typical bronchodilator medications. Primary causes include chronic rejection following lung or hematopoietic stem cell transplantation, exposure to toxic inhalants (like sulfur mustard gas or diacetyl), and certain autoimmune conditions, particularly rheumatoid arthritis.
Proliferative Bronchiolitis
Proliferative Bronchiolitis involves the formation of organizing intraluminal exudate, or plugs of granulation tissue, that partially or completely fill the bronchiolar lumen. This process is commonly seen as part of a larger disease called Organizing Pneumonia. Causes associated with this form include connective tissue disorders, chronic infections, and certain drug reactions. Proliferative forms are often more responsive to immunosuppressive treatments than the irreversibly scarred constrictive forms.
Diffuse Panbronchiolitis (DPB)
Diffuse Panbronchiolitis (DPB) is a chronic inflammatory disorder affecting the entire wall of the respiratory bronchioles throughout both lungs. This condition is overwhelmingly observed in individuals of East Asian descent, particularly in Japan and Korea, suggesting a strong genetic predisposition linked to the HLA-B54 type. DPB is characterized by chronic inflammation and the infiltration of inflammatory cells, which, if untreated, progresses to bronchiectasis and respiratory failure.
Recognizable Signs and Symptoms
The clinical presentation of adult bronchiolitis often develops slowly and worsens over months or years. The most common complaints are a persistent cough that may be dry or minimally productive, and progressive shortness of breath (dyspnea). This shortness of breath is typically noticeable first during physical exertion and then becomes constant as the disease progresses.
Patients often experience a non-reversible pattern of airflow obstruction, meaning breathing difficulty does not significantly improve after using a standard bronchodilator. Upon listening to the chest, a physician may hear crackles or sometimes a wheezing sound. The symptoms often overlap with more common conditions like chronic obstructive pulmonary disease (COPD) or asthma, which can delay an accurate diagnosis.
Diagnostic Procedures and Management
Diagnosing bronchiolitis in adults requires a multi-step approach because clinical symptoms alone are insufficient to confirm the disease.
Diagnosis
Pulmonary function tests (PFTs) are a standard initial tool, typically revealing an obstructive pattern with a reduced forced expiratory volume in one second (FEV1). PFTs also often show air trapping, reflected by an elevated residual volume, and a reduced diffusing capacity of the lung for carbon monoxide (DLCO).
High-Resolution Computed Tomography (HRCT) scanning of the chest is the most important non-invasive imaging test. HRCT often shows characteristic findings like air trapping on expiratory scans, appearing as patchy areas of decreased lung density in a pattern known as “mosaic perfusion.” While HRCT is highly suggestive, a definitive diagnosis, especially for determining the specific type of bronchiolitis, frequently requires a surgical lung biopsy.
Management
Management strategies are tailored to the specific form and underlying cause. For proliferative forms, treatment often involves immunosuppressive therapy, such as systemic corticosteroids, to reduce inflammation and halt the organizing process. Diffuse Panbronchiolitis has a specific treatment cornerstone: long-term, low-dose macrolide antibiotics like erythromycin, which are effective due to their anti-inflammatory properties. Treatment for Constrictive Bronchiolitis, particularly in advanced cases where irreversible scarring has occurred, is significantly limited and may progress to the consideration of lung transplantation.