Description

• Pulmonary fibrosis (PF) is an interstitial lung disease (ILD), a family of >200 different lung diseases, characterized by inflammation, cellular proliferation, and fibrosis within lung interstitium and bronchial walls. If no cause identified, ILD is called idiopathic interstitial pneumonia.
• The most common idiopathic interstitial pneumonia is idiopathic PF (IPF).
• IPF is defined as a form of progressive fibrotic ILD associated with the histologic and/or radiologic appearance of usual interstitial pneumonia (UIP) when other causes have been excluded.

Epidemiology

• Most common ILD prevalent worldwide (25–30% of all ILD)
• Most common in men >60 years of age

Incidence
Higher in North America and Europe (3 to 9 cases per 100,000 person-years) than in South America and East Asia (fewer than 4 cases per 100,000 person-years)

Prevalence
In the United States, the prevalence has been reported to range from 10 to 60 cases per 100,000 person-years.

Etiology and Pathophysiology

• A favored model for the pathogenesis of IPF is that recurrent, alveolar epithelial damage with accelerated cell senescence leads to abnormal cellular repair and deposition of interstitial fibrosis by myofibroblasts.
• Causes of nonidiopathic PF include occupational and environmental exposures, drugs, and connective tissue diseases.

Genetics

• The role of host genetic factors and their interactions with environmental factors is unknown.
• Mutations in genes involved in maintenance of telomere length are associated with increased risk of IPF.
• An SNP in the MUC5B promoter leads to gene overexpression and is associated with increased risk of IPF. However, the mechanism linking MUC5B and IPF is not clear.

Risk Factors

• Family history of IPF
• Smoking—most significant association
• GERD, OSA
• Occupational and environmental exposures: wood (pine), metal dusts (lead, brass, steel), farming, birds, hairdressing, stone cutting, exposure to livestock, vegetable and animal dust, air pollution, mold

General Prevention

Avoidance of above risk factors

Commonly Associated Conditions

• Pulmonary hypertension: 30–80% of patients with IPF
• GERD
• Nonidiopathic PF may be related to connective tissue diseases (RA and systemic sclerosis).