What Is Bronchiolitis Obliterans?

Bronchiolitis refers to the epithelial inflammatory response after bronchiole injury, and subsequent repairs lead to excessive proliferation of granulation tissue in the airway wall, air cavity, or both. Depending on the stage of the disease, the repair process can cause narrowing or distortion of the small airways (constrictive bronchiolitis) or complete occlusion (bronchiolitis obliterans (BO)). The alveoli adjacent to the small airway of the lesion are almost always affected, but most of the interstitial lung is not affected.

Bronchiolitis refers to the epithelial inflammatory response after bronchiole injury, and subsequent repairs lead to excessive proliferation of granulation tissue in the airway wall, air cavity, or both. Depending on the stage of the disease, the repair process can cause narrowing or distortion of the small airways (constrictive bronchiolitis) or complete occlusion (bronchiolitis obliterans (BO)). The alveoli adjacent to the small airway of the lesion are almost always affected, but most of the interstitial lung is not affected.

Chinese name

Occlusive bronchiolitis

Foreign name

bronchiolitis obliterans, obliterative bronchiolitis

Obstructive bronchiolitis I. Etiology and related diseases

BO is idiopathic and secondary, mostly secondary in pediatrics, and the common causes are as follows.

(1) Inhalation factors: such as poison gas, foreign body, gastro-esophageal reflux (GER), etc.

(2) Infectious factors: viruses, including adenovirus (types 3, 7, 21), respiratory syncytial virus, parainfluenza virus, influenza viruses A and B, and measles virus; bacteria, including Staphylococcus aureus, B Family hemolytic streptococcus, Streptococcus pneumoniae; Mycoplasma pneumoniae.

(3) Connective tissue diseases such as rheumatoid arthritis, exudative polyerythema (SJS), systemic lupus erythematosus, and dermatomyositis.

(4) Bone marrow transplantation, heart and lung transplantation after tissue and organ transplantation.

(5) Bronchial pulmonary dysplasia (BPD), congenital heart disease, and cystic fibrosis.

(6) Drugs.

Nowadays, the occurrence of BO is thought to be caused by various causes of epithelial cell damage. Due to the immune response, the epithelial cells undergo inflammatory response and fibrosis during the repair process.

Obstructive bronchiolitis II. Differential diagnosis

Lung biopsy is the gold standard for diagnosing BO. Due to the limitations of pathological examination, the diagnosis of BO is mainly clinical diagnosis, which mainly depends on clinical manifestations, imaging changes, abnormal lung function, and excludes other obstructive pulmonary diseases, which can be diagnosed through fiberbronchoscope. For example, it is now believed that after some causes such as inhalation injury, drugs, viruses, Mycoplasma pneumoniae, and some bacterial infections, persistent cough and wheezing or difficulty breathing, chest HRCT examinations have typical manifestations such as mosaic signs, gas trapping signs, peripheral bronchial Thickening and dilatation of the tube wall can be clinically diagnosed.

1. Asthma:

Both BO and asthma can occur after respiratory syncytial virus infection or severe pneumonia, and both have wheezing, and BO chest radiographs are usually not abnormal, or only manifested as hyperventilation, which is easily misdiagnosed as asthma. In addition, there are reports in the literature that we also found that during the HRCT examination of the chest of children with asthma, slight ground glass or mosaic signs may appear, which is easy to be misdiagnosed as BO. These two diseases can be identified based on the response of wheezing to bronchodilators and hormones, the history or family history of allergic diseases, and the performance of HRCT.

2. Occlusive bronchiolitis with organizing pneumonia (BOOP)

The pathogenesis and clinical manifestations are similar to BO, but the imaging findings are different. BOOP mainly manifests as patchy shadows in the lungs. BOOP's lung function is mostly a restrictive disorder. The most reliable identification is based on pathological examination, BO is the narrowing caused by scars outside the tube, and BOOP is the blockage of granulation tissue in the lumen.

3. Diffuse panbronchiolitis

Most patients with diffuse panbronchiolitis have sinusitis, and chest HRCT shows diffuse lung lobulous central nodules and bronchiectasis rather than mosaic signs and gas traps.

Obstructive bronchiolitis III. Examination

1. Lung function

Obstructive ventilation dysfunction is often irreversible, and the reversible test is negative.

2. Imaging performance

(1) X-ray

It shows that the lung is over-inflated, the blood vessel texture is thinner, and the ground glass is changed. There may be diffuse nodular or reticular nodular shadows, and no infiltrating shadows.

(2) High-resolution CT (HRCT)

Characteristic changes can show direct signs and indirect signs. Direct signs: peripheral bronchiolar wall thickening, bronchiectasis with retention of secretions, manifested as lobular central bronchial nodules. Indirect signs: peripheral bronchiectasis, insufficiency of lungs, markedly uneven lung density, high ventilation and low ventilation areas mixed (called mosaic form, also called mosaic perfusion), air retention signs. These changes are mainly in the lower lower lung and subpleura.

3.blood

About 40% of BO patients have varying degrees of hypoxemia, and blood gas can be used to assess the severity of the condition.

4. Pathological examination

Pathological examination is the most reliable diagnostic basis, but due to the risk of lung biopsy and the limitations of the location of the material, clinical development is difficult. Characteristic case changes of BO include bronchiectasis, wall thickening, inflammatory cell infiltration in small airways, hyperplasia of granulation tissue and fibrous tissue, bronchiolar inflammation and fibrosis, atelectasis, and decreased blood vessel volume and volume.

Occlusive bronchiolitis IV. Treatment

No specific treatment is available. The use of hormones is controversial. Given that the pathogenesis of BO is mediated by the immune response and a variety of inflammatory factors are involved, in recent years we have given methylprednisolone or prednisone treatment early according to the condition of the child, which has improved the clinical symptoms and pulmonary function of some children. Significant improvement in HRCT performance

According to the low-dose macrolides with anti-inflammatory effects and a variety of inflammatory factors involved in the pathogenesis of BO, some reports of BO patients treated with macrolides have improved clinical symptoms and pulmonary function.

Bronchodilators can be used to relieve asthma, and antibiotics can be used in cases of co-infection.