Causes of Pulmonary Fibrosis: Understanding the Underlying Factors Behind Lung Scarring

Pulmonary fibrosis is a complex and often progressive lung condition characterized by the thickening and scarring (fibrosis) of lung tissue, particularly in the interstitium—the network of tissue surrounding the air sacs. This scarring impairs the lungs' ability to transfer oxygen into the bloodstream, leading to symptoms like shortness of breath, dry cough, fatigue, and reduced exercise tolerance. While the exact mechanisms vary, understanding the root causes is essential for accurate diagnosis and effective treatment.

Known Causes of Pulmonary Fibrosis

Occupational and Environmental Exposures: One of the most well-documented causes of pulmonary fibrosis is long-term exposure to hazardous substances in certain work environments. This category includes pneumoconiosis (commonly known as "dust lung"), which affects individuals exposed to asbestos (asbestosis), silica (silicosis), or coal dust (coal worker's pneumoconiosis). These inhaled particles trigger chronic inflammation and gradual scarring of lung tissue.

Drug-Induced Lung Injury: Certain medications can lead to interstitial lung disease and subsequent fibrosis. Chemotherapy agents such as bleomycin and cyclophosphamide, some antibiotics (like nitrofurantoin), anti-arrhythmic drugs (such as amiodarone), and even specific biologic therapies have been linked to lung damage. The risk varies based on dosage, duration of use, and individual susceptibility.

Connective Tissue Diseases: Autoimmune and rheumatic disorders—including rheumatoid arthritis, systemic lupus erythematosus, scleroderma, and Sjögren's syndrome—can manifest with lung involvement. Interstitial lung disease associated with these conditions is a major cause of morbidity and mortality among patients with connective tissue diseases.

Idiopathic Interstitial Pneumonias

When no clear cause can be identified, the condition falls under the umbrella of idiopathic interstitial pneumonias (IIPs). Among these, idiopathic pulmonary fibrosis (IPF) is the most common and severe form. IPF primarily affects older adults and follows a progressive course, with median survival rates historically ranging from 3 to 5 years after diagnosis. Other types include nonspecific interstitial pneumonia (NSIP), which tends to have a better prognosis and may respond to immunosuppressive therapy.

Granulomatous Lung Diseases

Sarcoidosis:

Extrinsic Allergic Alveolitis (Hypersensitivity Pneumonitis):

Rare and Uncommon Causes

A number of less frequent but clinically significant conditions can also result in pulmonary fibrosis. These include:

• Pulmonary Alveolar Proteinosis (PAP): A rare disorder where surfactant-like material accumulates in the alveoli, impairing gas exchange and sometimes leading to secondary fibrotic changes.
• Goodpasture's Syndrome: An autoimmune condition involving both pulmonary hemorrhage and rapidly progressive glomerulonephritis, caused by antibodies attacking basement membranes in the lungs and kidneys.
• Lymphangioleiomyomatosis (LAM): A rare cystic lung disease affecting mostly women of childbearing age, associated with abnormal smooth muscle cell proliferation in the lungs.
• Idiopathic Pulmonary Hemosiderosis: Characterized by recurrent episodes of alveolar bleeding and iron deposition in lung tissue, eventually contributing to fibrosis.
• Chronic Eosinophilic Pneumonia: Marked by persistent infiltration of eosinophils in the lungs, this condition can mimic other forms of interstitial lung disease and may lead to structural lung damage if untreated.

Early detection and accurate classification of the underlying cause are crucial for managing pulmonary fibrosis effectively. Advances in imaging, biomarker research, and targeted therapies continue to improve outcomes, offering hope for better quality of life and prolonged survival for patients worldwide.