Understanding Pulmonary Fibrosis: Causes, Manifestations, and Management

What is pulmonary fibrosis?

Pulmonary fibrosis is a chronic lung disease characterized by progressive scarring and thickening of lung tissue. This process affects the interstitium, the delicate tissue surrounding the alveoli, where oxygen normally passes into the bloodstream. As fibrosis advances, the lungs lose elasticity, become stiff, and are less able to expand, leading to impaired gas exchange and increasing shortness of breath.

Pulmonary fibrosis is a progressive condition, but its course varies widely. Some individuals experience slow progression over many years, while others develop rapid deterioration. In many cases, especially in older adults, the underlying cause cannot be clearly identified. When no specific cause is found, the condition is classified as idiopathic pulmonary fibrosis (IPF).

The scarring associated with pulmonary fibrosis is irreversible. However, early diagnosis, appropriate medical therapy, and supportive interventions can slow disease progression, alleviate symptoms, and improve quality of life. In selected patients, lung transplantation may be considered.

Pathophysiology of pulmonary fibrosis

Pulmonary fibrosis develops when repeated injury to the lung tissue triggers abnormal healing responses. Instead of normal tissue repair, fibroblasts deposit excessive collagen and extracellular matrix, leading to permanent scarring. This thickened tissue disrupts oxygen diffusion, causing hypoxemia and increased respiratory effort.

Over time, reduced oxygen delivery strains the cardiovascular system and may lead to secondary complications, including pulmonary hypertension and right-sided heart failure.

Symptoms of pulmonary fibrosis

Symptoms usually develop gradually and worsen over time. Common clinical manifestations include:

• Progressive shortness of breath, initially during physical exertion and later at rest

• Persistent dry cough that does not produce mucus

• Extreme fatigue and reduced exercise tolerance

• Unintentional weight loss

• Aching muscles and joints

• Widening and rounding of the fingertips or toes, known as digital clubbing

In early stages, symptoms may be subtle and easily mistaken for aging or reduced physical fitness. As the disease advances, daily activities such as walking, dressing, or speaking for long periods may become difficult.

Causes of pulmonary fibrosis

Pulmonary fibrosis can result from a wide range of environmental, medical, and pharmacological factors. In many cases, multiple contributing mechanisms coexist.

Occupational and environmental exposures

Long-term or repeated exposure to inhaled toxins can damage lung tissue, especially in individuals who do not use adequate protective equipment. Harmful exposures include:

• Silica dust

• Asbestos fibers

• Hard metal dusts

• Wood, coal, and grain dust

• Mold spores

• Bird and animal droppings

Occupational risk is increased in mining, farming, construction, manufacturing, and animal handling.

Radiation therapy

Radiation treatment to the chest, commonly used for lung or breast cancer, can cause delayed lung injury. Radiation-induced pulmonary fibrosis may appear months or years after treatment. The severity depends on the radiation dose, the volume of lung exposed, and whether chemotherapy was administered concurrently.

Medication-induced lung injury

Several medications are known to cause lung toxicity, including:

• Chemotherapy agents such as methotrexate, bleomycin, and cyclophosphamide

• Antiarrhythmic drugs such as amiodarone

• Antibiotics such as nitrofurantoin and ethambutol

• Certain immunomodulatory and anti-inflammatory agents

Drug-induced fibrosis may improve if the medication is discontinued early, but in some cases lung damage persists.

Medical conditions associated with pulmonary fibrosis

Fibrosis can develop secondary to systemic diseases, particularly autoimmune and inflammatory disorders:

• Rheumatoid arthritis

• Systemic lupus erythematosus

• Scleroderma

• Polymyositis and dermatomyositis

• Mixed connective tissue disease

• Sarcoidosis

• Recurrent or severe pneumonia

These conditions may cause chronic inflammation that promotes fibrotic lung remodeling.

Idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis is diagnosed when no identifiable cause is found despite thorough evaluation. IPF primarily affects middle-aged and older adults and has a variable but often progressive course.

Risk factors associated with IPF include:

• Cigarette smoking

• Long-term exposure to air pollutants

• Gastroesophageal reflux disease (GERD)

• Genetic susceptibility

GERD is frequently observed in patients with IPF and may contribute to disease progression through repeated microaspiration, although its exact role remains under investigation.

Risk factors

Factors that increase the likelihood of developing pulmonary fibrosis include:

• Current or former smoking

• Occupational exposure to lung irritants

• Cancer treatments involving radiation or chemotherapy

• Autoimmune or connective tissue diseases

• Family history of pulmonary fibrosis

Although rare, pulmonary fibrosis can occur in children and infants, usually in association with genetic or developmental conditions.

Complications

As pulmonary fibrosis progresses, several serious complications may arise:

• Pulmonary hypertension, caused by increased resistance in lung blood vessels

• Right-sided heart failure due to chronic strain on the heart

• Respiratory failure resulting from critically low oxygen levels

• Increased risk of lung cancer

• Recurrent lung infections

• Blood clots or pneumothorax (collapsed lung)

Acute exacerbations, characterized by sudden worsening of shortness of breath over days or weeks, can occur, particularly in IPF. These episodes are medical emergencies and can be life-threatening.

Diagnosis

Diagnosis typically involves a combination of:

• Detailed medical history and exposure assessment

• Physical examination

• Pulmonary function tests

• High-resolution computed tomography (HRCT) of the chest

• Blood tests to evaluate autoimmune or inflammatory causes

In selected cases, lung biopsy may be necessary to confirm the diagnosis.

Management and treatment

Although lung scarring cannot be reversed, treatment aims to slow disease progression, manage symptoms, and prevent complications.

Management strategies may include:

• Antifibrotic medications that slow fibrosis progression

• Oxygen therapy for hypoxemia

• Pulmonary rehabilitation to improve exercise tolerance

• Treatment of underlying causes such as autoimmune disease or GERD

• Vaccination and infection prevention

For patients with advanced disease and suitable overall health, lung transplantation may be considered.

When to see a doctor

Medical evaluation is recommended for anyone experiencing persistent shortness of breath, chronic dry cough, or unexplained fatigue. Urgent medical attention is required if symptoms worsen rapidly, as this may indicate an acute exacerbation or infection.

Scientific references

1. King TE Jr, Pardo A, Selman M. Idiopathic pulmonary fibrosis. The Lancet. 2011;378(9807):1949–1961.

2. Raghu G, Remy-Jardin M, Myers JL, et al. Diagnosis of idiopathic pulmonary fibrosis. American Journal of Respiratory and Critical Care Medicine. 2018;198(5):e44–e68.

3. Lederer DJ, Martinez FJ. Idiopathic pulmonary fibrosis. New England Journal of Medicine. 2018;378:1811–1823.

4. Wells AU, Hirani N. Interstitial lung disease guideline. Thorax. 2008;63(Suppl V):v1–v58.

5. American Thoracic Society. Pulmonary fibrosis overview and management. ATS Clinical Practice Guidelines.