Introduction:
The clinical presentation and the history of pulmonary parenchymal disease may vary. Still, they are frequently considered collectively as they have similar signs, symptoms, pulmonary function abnormalities, and radiological changes. It comprises several diseases with known as well as unknown causes. The known diseases include collagen vascular diseases and environmental or drug-related diseases.
The unknown causes include idiopathic interstitial pneumonia, granulomatous parenchymal lung disease such as sarcoidosis, and other forms of parenchymal lung disease such as lymphangioleiomyomatosis, Langerhans histiocytosis X and eosinophilic pneumonia. Idiopathic interstitial pneumonia can further be classified as idiopathic pulmonary fibrosis (IPF), acute interstitial pneumonia (AIP), desquamative interstitial pneumonia (DIP), non-specific interstitial pneumonia (NSIP), respiratory bronchiolitis interstitial lung disease (RB-ILD), cryptogenic organizing pneumonia (COP) and lymphocytic interstitial pneumonia (LIP).
What Is Idiopathic Interstitial Pneumonia?
Idiopathic interstitial pneumonia is characterized by varying inflammation patterns and fibrosis in the lung parenchyma and comprises several contrasting clinicopathological entities. The most common type of idiopathic interstitial pneumonia is idiopathic pulmonary fibrosis.
What Is Idiopathic Pulmonary Fibrosis?
It is a condition in which the lungs become fibrotic or scarred. Scarring causes stiffness of the lungs, due to which breathing becomes difficult. It is a chronic, progressive, irreversible disorder that worsens over time, although the speed of worsening is highly variable. It usually affects individuals above 50 years.
Cause:
Idiopathic means the cause is unknown. However, there are a variety of reasons that can cause idiopathic pulmonary fibrosis:
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Viral infections like the Ebstein-Barr virus.
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Occupational hazards include exposure to certain types of dust, wood, and metals.
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Chronic gastroesophageal reflux disease (GERD).
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Drugs such as antidepressants.
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Cigarette smoking.
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Familial history of IPF, although rare.
Clinical Presentation:
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Breathlessness.
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Non-productive cough.
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Clubbing or rounded swelling of fingertips.
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Tiredness.
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Weight loss.
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Bi-basal fine late inspiratory crackles, unlike velcro.
Lab Investigations:
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Pulmonary Function Tests: Show a restrictive defect with reduced lung volumes and gas exchange.
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Bronchoalveolar Lavage: It can be used to rule out other conditions
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High-Resolution Computed Tomography (HRCT): It gives a more detailed picture of the lung than traditional chest X-ray and conventional computed tomography (CT) scan. It can reveal the presence of scar tissue and the extent of lung damage. It typically demonstrates a patchy, predominantly peripheral, subpleural, and basal reticular pattern with subpleural cysts and traction bronchiectasis.
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Lung Biopsy: It is not usually required in those with typical clinical features and HRCT appearances but may be required in cases with atypical features.
Management: Treatment is quite challenging. Prednisolone, along with Azathioprine, is recommended for patients who are highly symptomatic or have rapidly progressive disease. Lung transplants should be considered in young patients with advanced diseases. Oxygen therapy may be required for palliation of breathlessness.
What Is Desquamative Interstitial Pneumonia?
It is characterized by numerous pigmented macrophages in most of the distal part of the lung or the alveolus, and sometimes, there is the presence of giant cells as well. The macrophages have abundant eosinophilic cytoplasm and contain fine granular, light brown pigment. It is usually associated with smokers, especially men between the ages of 40 and 60.
Causes:
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Smoking.
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Exposure to copper, beryllium, fumes, and fire extinguisher powder.
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Nylon filaments in textile workers.
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Autoimmune diseases like scleroderma and rheumatoid arthritis.
Pathophysiology:
Accumulation of macrophages in response to smoking. The characteristic finding of pigmented macrophages has a distinctive bronchiolocentric distribution with centrilobular ground glass opacities in chest imaging.
Clinical Presentation:
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Non-productive cough.
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Clubbing or swollen fingertips in 50 % of the patients.
Lab Investigation:
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Pulmonary Function Test: It shows restrictive defects with impaired diffusion capacity.
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Peripheral Blood Smear: It may reveal an increase in neutrophil and eosinophil count.
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Chest X-Ray: It shows reticulonodular infiltrates in lower lung zones.
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HRCT: Shows diffuse bilateral lower lobe predominant ground glass changes in a homogeneous pattern without a honeycomb appearance. It is the best imaging modality over others. In progressive disease, cysts and traction bronchiectasis may be seen, but not exclusively subpleural.
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Lung Biopsy: Shows increased macrophages in the alveolar space, septal thickening, and type 2 pneumocyte hyperplasia.
Treatment: Systemic corticosteroids and immunosuppressive therapy, with Azathioprine being most commonly used, remain the mainstay of treatment. The prognosis is generally good. Avoidance of smoking and exposure remains the key to preventing disease progression.
What Is Cryptogenic Organizing Pneumonia (COP)?
It is a rare lung disease affecting the bronchioles and alveoli. It is also known as bronchiolitis obliterans organizing pneumonia. It equally affects the male and female populations between 50-60 years of age.
Clinical Presentation:
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Persistent cough.
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Fever.
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Malaise.
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Weight loss.
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Exertional dyspnea.
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Clubbing is absent.
Lab Investigation:
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Chest X-Ray: It shows bilateral, diffuse, peripherally distributed alveolar opacities with normal lung volume.
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HRCT: It shows patchy consolidation, ground glass opacities, small nodular opacities, bronchial wall thickening, and dilation.
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Peripheral Blood Smear: Leukocytosis with a marked increase in erythrocyte sedimentation rate( ESR) is commonly seen.
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Lung biopsy: Shows florid proliferation of mature collagen or Masson bodies and fibrous tissue.
Treatment: Response to systemic corticosteroids is classically excellent.
What Is Acute Interstitial Pneumonia?
A viral upper respiratory tract infection often precedes it. There is no gender preference, and it exhibits a bimodal distribution that can involve children as young as seven years and elderly patients over 80 years. It is characterized by the sudden onset of dyspnea and rapid development of respiratory failure.
Clinical Presentation:
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Viral prodromal features.
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Exertional dyspnea.
The gross appearance is quite similar to patients with acute respiratory distress syndrome. In the early stages, the lung is firm, heavy, and dark red in appearance, whereas in later stages, it becomes very heavy with irregular areas of dense consolidation and fibrosis.
Lab Investigation:
HRCT: Shows bilateral and symmetric, diffuse ground glass and alveolar consolidation opacities. Traction bronchiectasis and bronchiolectasis may appear with the progression of the disease.
Lung Biopsy: It shows pneumonic consolidation and diffuse alveolar damage.
Treatment: There are no specific treatments for acute interstitial pneumonia, and only supportive management can be provided. The prognosis is often poor, and the mortality rate is more than 50 %.
What Is Respiratory Bronchiolitis Interstitial Lung Disease?
It is a mild inflammatory pulmonary disease that occurs more commonly in men and heavy smokers, usually between 40-60 years of age. It is usually characterized by shortness of breath and cough production.
Pulmonary Function Test: Shows obstructive, restrictive, or mixed patterns.
HRCT: Shows centrilobular micronodules, ground glass opacities, and peribronchiolar thickening.
Treatment: Smoking cessation may lead to improvement, and systemic corticosteroid therapy has proven to be the mainstay of treatment.
Conclusion:
Pulmonary parenchymal disease is a group of conditions affecting the interstitium and the alveolar lumen. It is commonly present as dyspnea and diffuse infiltrates on chest X-rays. HRCT is the key diagnostic modality, and a lung biopsy may be required in cases with atypical features. Corticosteroid therapy is the drug of choice. Oxygen may be provided as a palliative treatment.
