From the Guidelines
Bronchiolitis obliterans is primarily caused by inflammation and scarring of the bronchioles due to various insults, including infections, inhaled toxins, autoimmune disorders, and complications from organ transplantation, as noted in the British Thoracic Society guideline for the use of long-term macrolides in adults with respiratory disease 1.
Causes of Bronchiolitis Obliterans
The causes of bronchiolitis obliterans can be categorized into several key areas:
- Inhalation of toxic chemicals or gases, such as diacetyl found in microwave popcorn flavoring, leading to conditions like "popcorn lung"
- Respiratory infections, particularly those caused by adenovirus, influenza, or respiratory syncytial virus
- Autoimmune disorders, including rheumatoid arthritis
- Adverse drug reactions
- Complications from organ transplantation, especially lung or bone marrow transplants, where it manifests as chronic rejection
- Chronic aspiration of stomach contents into the lungs
- Certain connective tissue diseases
Pathophysiology and Clinical Presentation
The inflammation process leads to fibrosis and narrowing of the bronchioles, resulting in irreversible airflow obstruction. This condition causes symptoms like progressive shortness of breath, dry cough, wheezing, and fatigue. The damage occurs when the body's immune response to these triggers becomes excessive, leading to destruction of the epithelial cells lining the airways and subsequent scarring that permanently narrows the bronchioles, as discussed in the international ISHLT/ATS/ERS clinical practice guideline for the diagnosis and management of bronchiolitis obliterans syndrome 1.
Diagnosis and Management
Diagnosis of bronchiolitis obliterans syndrome (BOS) requires careful exclusion of other post-transplant complications that can cause delayed lung allograft dysfunction. The management of BOS involves various therapeutic interventions, including the use of systemic corticosteroids, cyclosporine, tacrolimus, and azithromycin, as well as re-transplantation in some cases, as outlined in the guideline 1. However, it's crucial to note that currently available therapies have not been proven to result in significant benefit in the prevention or treatment of BOS, highlighting the need for further research to identify optimal therapies and effective strategies for its prevention 1.
From the Research
Causes of Bronchiolitis Obliterans (Constrictive Bronchiolitis)
The causes of Bronchiolitis Obliterans (Constrictive Bronchiolitis) can be attributed to several factors, including:
- Alloimmunologic injury marked by clinically apparent acute rejection episodes 2
- Inflammatory conditions, including viral infections or ischemic injury 2
- Chronic immunologic/inflammatory insults leading to peri-bronchiolar leukocyte infiltration, with a subsequent exuberant tissue re-modelling and fibro-obliteration of the luminal space of the allograft airways 3
- Systemic graft-versus-host disease (GVHD) in hematopoietic cell transplantation (HCT) 4
- Adverse drug reaction, toxic inhalation, and autoimmune disorders 5
- Certain pulmonary infections 5
Risk Factors
Risk factors for bronchiolitis obliterans include: