Definition and epidemiology
Pulmonary fibrosis refers to a group of chronic lung diseases characterized by progressive deposition of fibrous connective tissue in the pulmonary interstitium, leading to irreversible architectural distortion and restrictive lung physiology. The term encompasses idiopathic pulmonary fibrosis (IPF), the most common and severe form, as well as fibrosis secondary to connective tissue disease, drugs, radiation, occupational exposures, or chronic hypersensitivity pneumonitis.
IPF is a disease of older adults, with most patients diagnosed between ages 60 and 70. It is rare before age 50 and shows a male predominance (roughly 2:1). Estimated prevalence is approximately 10-60 cases per 100,000 persons, varying by region and case definition, with incidence rising over recent decades, partly from improved recognition.
- Median survival after diagnosis of IPF historically ranged 3-5 years, though antifibrotic therapy has improved this
- Smoking history is present in a majority of IPF patients
- Familial pulmonary fibrosis accounts for a small subset, often linked to telomere-related gene mutations
- UIP pattern on HRCT = basal, subpleural honeycombing + traction bronchiectasis, no biopsy needed if classic
- PFTs show restrictive pattern with reduced DLCO out of proportion to volume loss
- Pirfenidone and nintedanib slow FVC decline in IPF; neither reverses fibrosis
- Corticosteroids/immunosuppressants are NOT indicated for IPF but ARE used in CTD-associated ILD
- MUC5B promoter polymorphism is the strongest known genetic risk factor for IPF
- Acute exacerbation = rapid dyspnea worsening + new ground-glass opacities on background fibrosis
- Lung transplant is the only therapy shown to improve survival in advanced IPF
- Clubbing and Velcro crackles at the lung bases are classic exam findings
Etiology and risk factors
IPF is, by definition, idiopathic, but several risk factors are strongly associated:
- Cigarette smoking (current or former)
- Age over 60
- Male sex
- Genetic predisposition: mutations in telomerase genes (TERT, TERC) and the MUC5B promoter polymorphism are the best-characterized genetic risk factors
- Occupational and environmental exposures: wood dust, metal dust, silica
- Chronic microaspiration/gastroesophageal reflux disease (proposed contributor)
Secondary (non-idiopathic) causes of pulmonary fibrosis
| Category | Examples |
|---|---|
| Connective tissue disease | Rheumatoid arthritis, systemic sclerosis, dermatomyositis, Sjogren syndrome |
| Drug-induced | Amiodarone, methotrexate, nitrofurantoin, bleomycin |
| Occupational/environmental | Asbestosis, silicosis, chronic hypersensitivity pneumonitis (bird/mold antigens) |
| Radiation | Prior thoracic radiotherapy |
| Sarcoidosis | End-stage fibrotic sarcoidosis |
Distinguishing IPF from these secondary causes is essential because management and prognosis differ.
Pathophysiology
The current model of IPF pathogenesis holds that repeated micro-injury to alveolar epithelial cells, in a genetically susceptible and aging lung, triggers an aberrant wound-healing response rather than classic chronic inflammation. Injured type II pneumocytes release profibrotic mediators (notably TGF-beta) that activate fibroblasts, which differentiate into myofibroblasts and deposit excess extracellular matrix (collagen).
This process produces the histologic and radiologic pattern of usual interstitial pneumonia (UIP): patchy, temporally heterogeneous fibrosis with fibroblastic foci, honeycomb cysts, and a subpleural, basal-predominant distribution. The resulting architectural distortion:
- Reduces lung compliance, producing a restrictive ventilatory defect
- Thickens the alveolar-capillary membrane, impairing diffusion (reduced DLCO)
- Causes ventilation-perfusion mismatch and progressive hypoxemia, especially with exertion
Unlike many interstitial lung diseases, inflammation is not the primary driver in IPF, which explains the limited efficacy of immunosuppressants and the rationale for antifibrotic agents.
Clinical features
Onset is insidious, often over months to years, which commonly delays diagnosis.
- Progressive exertional dyspnea (the dominant and earliest symptom)
- Persistent dry, nonproductive cough
- Fatigue and, in later stages, weight loss
- Bibasilar fine inspiratory crackles ('Velcro crackles') on auscultation, often first found at the lung bases
- Digital clubbing (present in a substantial minority)
- Signs of pulmonary hypertension or cor pulmonale in advanced disease (loud P2, lower extremity edema)
Acute exacerbations can occur: a rapid, unexplained worsening of dyspnea over days to weeks with new ground-glass opacities on imaging superimposed on the baseline fibrotic pattern, carrying a high short-term mortality.
Diagnosis
Diagnosis of IPF requires exclusion of known causes of interstitial lung disease plus either a characteristic HRCT pattern or histopathology, established through multidisciplinary discussion among pulmonology, radiology, and pathology.
Initial workup
- Detailed history: exposures, drugs, connective tissue disease symptoms, family history
- Serologic screening for connective tissue disease (ANA, rheumatoid factor, anti-CCP, myositis panel) to exclude secondary causes
- Pulmonary function tests: restrictive pattern (reduced FVC and TLC, normal or increased FEV1/FVC ratio) with reduced DLCO
- High-resolution CT (HRCT) chest: the key diagnostic test
HRCT findings in UIP pattern
- Subpleural and basal predominant reticulation
- Honeycombing (clustered subpleural cysts)
- Traction bronchiectasis/bronchiolectasis
- Absence of features suggesting an alternative diagnosis (extensive ground-glass, nodules, cysts away from honeycombing)
If HRCT shows a definite UIP pattern in the right clinical context, surgical lung biopsy is generally unnecessary. Indeterminate or atypical patterns may warrant biopsy (surgical or transbronchial cryobiopsy) or genomic classifier testing where available. Six-minute walk test assesses exertional desaturation and prognosis.
Differential diagnosis
- Hypersensitivity pneumonitis (chronic): history of antigen exposure, upper/mid-zone predominance, mosaic attenuation
- Connective tissue disease-associated interstitial lung disease: positive autoantibodies, extrapulmonary features
- Nonspecific interstitial pneumonia (NSIP): more ground-glass, less honeycombing, often better prognosis
- Asbestosis: occupational exposure history, pleural plaques
- Sarcoidosis (fibrotic stage): upper lobe predominance, lymphadenopathy
- Chronic heart failure: can mimic dyspnea and basal crackles; echo and BNP help differentiate
- COPD/emphysema (combined pulmonary fibrosis and emphysema syndrome can coexist)
Management
Management goals are to slow fibrosis progression, manage symptoms and comorbidities, and consider transplantation in eligible candidates. Guideline bodies (ATS/ERS/JRS/ALAT and others) broadly agree on antifibrotic therapy for IPF; management of secondary fibrosis instead targets the underlying disease.
Pharmacologic
- Antifibrotic agents, pirfenidone or nintedanib, are first-line for IPF; both slow the rate of decline in FVC but do not reverse established fibrosis
- Immunosuppressants (corticosteroids, azathioprine) are not recommended for IPF but are used in connective tissue disease-associated or inflammatory forms of fibrosing ILD
- Treatment of underlying cause when secondary (discontinue offending drug, treat connective tissue disease, remove exposure)
- Antacid therapy for reflux is no longer routinely recommended given lack of clear benefit in recent guidance
Non-pharmacologic
- Supplemental oxygen for resting or exertional hypoxemia
- Pulmonary rehabilitation to improve exercise capacity and quality of life
- Vaccination (influenza, pneumococcal, COVID-19) to reduce infectious triggers of exacerbation
- Smoking cessation
- Early referral for lung transplant evaluation in appropriate candidates, as it remains the only intervention shown to extend survival in advanced disease
- Palliative care involvement for symptom control (dyspnea, cough) as disease progresses
Acute exacerbations are typically managed with high-dose corticosteroids and exclusion of infection, though evidence for steroid benefit is limited.
Complications and prognosis
- Progressive respiratory failure is the most common cause of death
- Pulmonary hypertension and cor pulmonale
- Acute exacerbations, which carry high in-hospital mortality
- Increased risk of lung cancer
- Venous thromboembolism (modestly increased risk)
- Secondary pneumothorax (less common)
Prognosis is variable but generally poor without antifibrotic therapy or transplant; historical median survival was 3-5 years from diagnosis. Decline in FVC and DLCO over time, degree of honeycombing, and episodes of acute exacerbation are the strongest prognostic markers. Antifibrotic therapy slows functional decline but is not curative.
"CARDS" for causes of upper-lobe fibrosis vs IPF's lower-lobe pattern: Coal worker's pneumoconiosis, Ankylosing spondylitis, Radiation, Diseases (sarcoid, histiocytosis), Silicosis/TB — remember IPF itself is classically BASAL, so upper-lobe fibrosis should prompt you to think of this list instead.
Practice questions
1. A 68-year-old man presents with a 1-year history of progressive exertional dyspnea and dry cough. He has a 40-pack-year smoking history. Exam reveals bibasilar fine inspiratory crackles and clubbing. Pulmonary function tests show FVC 65% predicted, FEV1/FVC 85%, and DLCO 50% predicted. HRCT shows subpleural, basal-predominant reticulation with honeycombing and traction bronchiectasis, no ground-glass opacities. Which of the following is the most appropriate next step in management?
2. A 55-year-old woman with a history of rheumatoid arthritis presents with progressive dyspnea. HRCT shows bibasilar reticular opacities with some ground-glass changes but minimal honeycombing. Autoimmune serologies are positive for rheumatoid factor and anti-CCP antibody. Which of the following best describes the most likely underlying process?
3. A 71-year-old woman with known IPF on nintedanib presents with acute worsening of dyspnea over the past 5 days. Chest CT shows new bilateral ground-glass opacities superimposed on her known basal honeycombing, without evidence of infection, heart failure, or pulmonary embolism on workup. Which of the following best characterizes this presentation?
Frequently asked questions
What causes pulmonary fibrosis?
Idiopathic pulmonary fibrosis has no identified single cause but is linked to aging, cigarette smoking, and genetic factors like the MUC5B promoter variant and telomerase gene mutations. Secondary pulmonary fibrosis can result from connective tissue disease, certain drugs (amiodarone, methotrexate, nitrofurantoin), occupational dust exposure (asbestos, silica), chronic hypersensitivity pneumonitis, or prior radiation therapy.
What are the first symptoms of pulmonary fibrosis?
The earliest and most common symptom is progressive shortness of breath with exertion, which develops gradually over months to years. A persistent dry cough often accompanies it. Fatigue is also common early on. Because these symptoms are nonspecific, diagnosis is frequently delayed until crackles are heard on exam or imaging is obtained.
How is pulmonary fibrosis diagnosed?
Diagnosis combines clinical history, pulmonary function tests showing a restrictive pattern with reduced DLCO, and high-resolution CT of the chest looking for a usual interstitial pneumonia pattern (basal honeycombing, traction bronchiectasis). Blood tests exclude connective tissue disease as a secondary cause. If HRCT findings are atypical, lung biopsy or multidisciplinary review may be needed to confirm the diagnosis.
Is pulmonary fibrosis curable?
No, pulmonary fibrosis is not curable; established scarring is permanent. Antifibrotic medications (pirfenidone, nintedanib) can slow the rate of lung function decline but do not reverse existing fibrosis. Lung transplantation is the only treatment that can meaningfully extend survival in eligible patients with advanced disease.
Pulmonary fibrosis vs COPD — what is the difference?
Pulmonary fibrosis causes a restrictive lung pattern with reduced lung volumes and reduced DLCO, from scarring of lung tissue, while COPD causes an obstructive pattern with air trapping and increased lung volumes, from airway narrowing and emphysema. Imaging also differs: fibrosis shows basal reticulation and honeycombing, while COPD shows hyperinflation and emphysematous changes. The two conditions can coexist as combined pulmonary fibrosis and emphysema.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: J84.1
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.