Interstitial lung disease !
Interstitial lung disease is a group of disorders that inflame and scar the tissue around the lungs' air sacs, causing growing breathlessness.
Updated 2026-10-29
Structures involved
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- Right lower lobe
- Left lower lobe
- Pleura
- Pulmonary arteries
- Right ventricle
- Segmental lung vessels
- Segmental bronchi
In biochemistry
In the clinical exam
- Digital clubbing and nail signs
- Adventitious sounds: crackles, wheezes, rhonchi, stridor and pleural rub
In physiology
- Lung volumes, capacities and spirometry
- Obstructive and restrictive patterns, and flow–volume loops
- The causes of hypoxemia
- Lung and chest wall compliance
- Diffusion across the respiratory membrane and DLCO
- The work of breathing
Why it happens
- Fibrosis in organs: TGF-β and the myofibroblast
- Air pollution and occupational exposures
- Ionizing radiation injury
- The alveolus: type I and II pneumocytes, surfactant, the blood–air barrier
What it is
A group of disorders that inflame and scar the lung interstitium around the alveoli, causing progressive breathlessness. Idiopathic pulmonary fibrosis is the most typical form.
Who gets it
Idiopathic pulmonary fibrosis affects mostly older men with a history of smoking. Connective tissue disease, hypersensitivity pneumonitis (birds, moulds) and occupational dust exposures are other frequent causes in the region.
Causes
- Idiopathic: idiopathic pulmonary fibrosis and other idiopathic interstitial pneumonias
- Connective tissue disease: rheumatoid arthritis, systemic sclerosis, myositis, lupus
- Hypersensitivity pneumonitis: birds, moulds, organic dusts
- Occupational: silica, asbestos, coal dust
- Drugs and radiation: some antiarrhythmics, chemotherapy and antimicrobials
- Sarcoidosis
Risk factors
- Older age (idiopathic pulmonary fibrosis)
- Smoking
- Occupational or environmental exposure
- Connective tissue disease
- Gastro-oesophageal reflux
- Family history
Pathophysiology
Repeated injury to the alveolar lining leads to abnormal repair, with fibroblast activation and collagen deposition in the interstitium. The lung becomes stiff and small (restrictive) and gas transfer falls. Advanced fibrosis creates honeycombing and can cause pulmonary hypertension.
Classification
- Idiopathic pulmonary fibrosis (usual interstitial pneumonia pattern)
- Other idiopathic interstitial pneumonias (for example nonspecific interstitial pneumonia)
- Connective tissue disease-related
- Exposure-related (hypersensitivity pneumonitis, pneumoconioses, drugs)
- Granulomatous (sarcoidosis)
Symptoms and signs
- Progressive breathlessness on exertion
- Dry cough
- Fine inspiratory crackles at the lung bases (velcro-like)
- Finger clubbing, mainly in idiopathic pulmonary fibrosis
- Fatigue and weight loss
Diagnosis
- Clinical
- Breathlessness with basal crackles; a careful exposure, drug and rheumatological history. A multidisciplinary team agrees the final diagnosis.
- Tests
- Lung function tests with a restrictive pattern and reduced gas transfer (DLCO); six-minute walk with oximetry; autoantibodies; bronchoalveolar lavage or lung biopsy in selected cases.
- Imaging
- High-resolution CT is key: in idiopathic pulmonary fibrosis, basal subpleural reticulation, traction bronchiectasis and honeycombing. Chest X-ray may show reticular shadowing.
Differential diagnosis
- Heart failure
- COPD
- Atypical pneumonia
- Lymphangitic spread of cancer
- Pulmonary tuberculosis
Goal of treatment
Slow the scarring, treat the cause or inflammation, relieve symptoms and plan transplant or palliative care in time.
Treatment
- Medical
- Antifibrotic drugs for idiopathic pulmonary fibrosis and other progressive fibrosing forms.
- Medical
- Corticosteroids and other immunosuppressants for inflammatory forms (connective tissue disease, hypersensitivity pneumonitis); they are not used for idiopathic pulmonary fibrosis.
- Lifestyle
- Avoidance of the trigger (birds, moulds, dust, culprit drug) and smoking cessation; vaccination.
- Rehabilitation
- Pulmonary rehabilitation and oxygen therapy for hypoxaemia.
- Surgical
- Lung transplantation for suitable patients with progressive disease.
Complications
- Respiratory failure
- Pulmonary hypertension and cor pulmonale
- Acute exacerbation
- Lung cancer
- Infections and pneumothorax
Prognosis
Varies by type. Idiopathic pulmonary fibrosis has a poor prognosis, with survival often measured in years; inflammatory and exposure-related forms can stabilise if treated early.
Prevention
- Avoiding smoking and protecting workers from mineral and organic dusts
- Monitoring lungs in connective tissue disease and with high-risk drugs
Test yourself
Think of the answer, then tap the question to see it.
What lung function pattern is typical of interstitial lung disease?
A restrictive pattern with reduced lung volumes and reduced gas transfer (DLCO).
Which CT findings suggest idiopathic pulmonary fibrosis?
Basal, subpleural reticulation with honeycombing and traction bronchiectasis (usual interstitial pneumonia pattern).
What chest sound is typical of pulmonary fibrosis?
Fine, dry inspiratory crackles at the lung bases, often described as velcro-like.
Which drug group slows idiopathic pulmonary fibrosis?
Antifibrotic drugs; corticosteroids are not used for idiopathic pulmonary fibrosis.
Related conditions
- Rheumatoid arthritis
- Systemic lupus erythematosus
- Heart failure
- Chronic obstructive pulmonary disease (COPD)
- Gastro-oesophageal reflux disease (GERD)
- Lung cancer
- Pulmonary tuberculosis
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Interstitial Lung Disease (StatPearls (NCBI Bookshelf), 2026).
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