Introduction
Bronchiolitis obliterans organizing pneumonia (BOOP) is a rare lung disorder that was described in the early 1980s as a distinct clinicopathologic syndrome and is characterized by a subacute or chronic respiratory illness. The term bronchiolitis obliterans refers to plugs or swirls of fibrous, granulation tissue filling the bronchioles, and organizing pneumonia refer to swirls of granulation tissue filling the alveoli and alveolar ducts. Though the term pneumonia is used, bronchiolitis obliterans organizing pneumonia (BOOP) is not an infection. Bronchiolitis obliterans organizing pneumonia (BOOP) has been reported all over the world, which affects both men and women.
What Are the Causes of Bronchiolitis Obliterans Organizing Pneumonia (BOOP)?
The causes of bronchiolitis obliterans organizing pneumonia (BOOP) are idiopathic (unknown). Idiopathic BOOP is also called cryptogenic organizing pneumonia and Epler’s pneumonia. The most common causes are radiation therapy, exposure to birds, post-respiratory infections, post-organ transplantation, exposure to certain chemicals or fumes, and some medications.
Certain systemic disorders are found to be associated with bronchiolitis obliterans organizing pneumonia (BOOP), including inflammatory bowel disease (a condition that causes swelling of the lining of the intestine), connective tissue disorder, immunological disorders, lung cancer, lung abscess, lymphoma (cancer of the lymphatic system), and idiopathic pulmonary fibrosis (it is a pulmonary condition characterized by the scarring of the lungs).
What Are the Signs and Symptoms of Bronchiolitis Obliterans Organizing Pneumonia (BOOP)?
The symptoms of bronchiolitis obliterans organizing pneumonia (BOOP) vary from person to person. They are:
- Influenza-like illness.
- Non-productive cough (a cough without sputum).
- Low-grade pyrexia (fever).
- Dyspnea (shortness of breath).
- Malaise (feeling of not well).
- Weight loss.
- Sore throat.
- Fatigue (tiredness).
- Pleuritic chest pain.
- Hemoptysis (coughing up blood mixed with sputum).
What Are the Some of the Imaging Procedures Used to Diagnose Bronchiolitis Obliterans Organizing Pneumonia (BOOP)?
Some of the imaging procedures used to diagnose bronchiolitis obliterans organizing pneumonia (BOOP) are as follows:
Plain Radiography:
- In plain radiograph, bronchiolitis obliterans organizing pneumonia (BOOP) appears as unilateral or bilateral patchy consolidated alveolar airspace.
- It commonly occurs in the lower zones of the subpleural or peribronchial area.
- Consolidation is found as nonsegmental and is two to six centimeters in diameter.
- Miliary shadowing and basal irregular linear opacities are also seen.
- In half of the patients, nodules are seen, which are three to five millimeters in diameter, and unilateral lobar or focal consolidation is seen in 5 to 31 percent of patients.
- Pleural thickening occurs in 13 percent of patients, and pleural effusions are rarely present.
- An air bronchogram might be present.
- The infiltrates enlarge gradually from their original size, or new infiltrates start appearing.
Computed Tomography (CT) Scan:
- Patchy ground glass opacities were found in peri broncho vascular distribution (80 percent) and subpleural areas.
- In the areas of air bronchogram, cylindrical bronchial dilatation and bronchial wall thickening are seen in computed tomography scans.
- Bilateral basal airspace consolidation is seen in 71 percent of patients
- Cavitating lung mass is rare, and pleural effusion is seen in about 33 percent of patients.
- Mediastinal lymphadenopathy and centrilobular nodules (three to five millimeters) are seen.
- Small, ill-defined nodular opacity measuring about one to ten millimeters in diameter is seen in the CT scan.
- Reversed halo sign is mainly described as or characterized by a focal round area of a ground glass opaque area surrounded by a ring (more than three-fourths of a circle) of consolidation seen in a CT scan. The consolidation should be at least two millimeters thick.
- Single or multiple focal lesions are less often seen.
- The early radiographic and clinical findings of BOOP are similar to that of interstitial pneumonitis.
As the prognosis of interstitial pneumonitis is poor, it is important to distinguish them. Some of the distinguishing features are:
- High-resolution computed tomography (HRCT) shows interlobular septal thickening, traction bronchiectasis, and intralobular reticular are more prevalent in interstitial pneumonitis than in bronchiolitis obliterans organizing pneumonia (BOOP).
- Peripheral distribution and lung parenchymal nodules are more prevalent in BOOP than in interstitial pneumonitis.
- Ground glass appearance, architectural distortion, and airspace consolidation are common for BOOP and interstitial pneumonitis.
Magnetic Resonance Imaging (MRI) Scan:
- MRI has a lesser role in diagnosing bronchiolitis obliterans organizing pneumonia (BOOP) but plays a role in follow-up imaging in BOOP patients to assess the disease activity and treatment response.
- In gadolinium-enhanced T1 weighted MRI, chronic inflammatory lung diseases such as sarcoidosis (growth of small collections of inflammatory cells in different body parts), bronchiolitis obliterans organizing pneumonia (BOOP), and bronchoalveolar carcinoma appear as an enhanced lesion.
- Sometimes heavily T2-weighted images of MRI can show white lung signs in bronchiolitis obliterans organizing pneumonia (BOOP) patients.
What Are the Treatment Options for Bronchiolitis Obliterans Organizing Pneumonia (BOOP)?
The treatment options for bronchiolitis obliterans organizing pneumonia (BOOP)
- Sometimes the symptoms of bronchiolitis obliterans organizing pneumonia (BOOP) may resolve without any treatment, especially when it is a post-breast radiation therapy type.
- In individuals with mild disease or non-progressive disease, the disease process can be monitored, and treatment can be done if required.
- Medications such as anti-inflammatory drugs and corticosteroids (Prednisolone) are usually given. With this medication, the patient's symptoms can resolve within a few days or weeks.
- Sometimes, BOOP may recur when the dose is decreased and is treated by giving additional doses.
- When the disease shows rapid progression, intravenous corticosteroids and Cytoxan are helpful.
- For individuals with secondary BOOP, the primary disease condition needs to be treated first, along with additional symptomatic and supportive therapy.
- Other drugs such as Erythromycin (Azithromycin), Cyclophosphamide, and Mycophenolate mofetil are used for patients who are not responding to steroid therapy.
- In rare cases, lung transplantation is required when the patient is not responding to standard treatment options.
Conclusion:
High-resolution computed tomography (HRCT) is an effective imaging modality in diagnosing BOOP. HRCT is highly specific in imaging the bronchiolitis obliterans organizing pneumonia (BOOP) than plain radiographs and computed tomography (CT). Bronchiolitis obliterans organizing pneumonia (BOOP) is commonly found in the age group between 40 to 60 years old however it can affect any age group. It is estimated that bronchiolitis obliterans organizing pneumonia (BOOP) is found in five to ten percent of chronic infiltrative lung disorders in the United States.
