Orientation notes for study. Specialist diagnosis uses a multidisciplinary team; check local guidelines before prescribing.
Definition
Interstitial lung diseases (ILD), or diffuse parenchymal lung diseases, are a heterogeneous group of more than 200 disorders that cause inflammation and/or fibrosis of the lung interstitium (alveolar walls and the tissue around airways and vessels). They produce a restrictive pattern of lung function and impaired gas exchange.
Classification
| Group | Examples |
|---|---|
| Idiopathic interstitial pneumonias | Idiopathic pulmonary fibrosis (IPF), nonspecific interstitial pneumonia (NSIP), cryptogenic organising pneumonia (COP), desquamative interstitial pneumonia |
| Known cause | Occupational (silica, asbestos, coal), drugs (amiodarone, methotrexate, nitrofurantoin, bleomycin), radiation, hypersensitivity pneumonitis (farmer's lung, bird fancier's lung) |
| Connective tissue disease–related | Rheumatoid arthritis, systemic sclerosis, SLE, myositis, Sjögren's |
| Granulomatous | Sarcoidosis |
| Rare | Eosinophilic pneumonia, pulmonary alveolar proteinosis, LAM, Langerhans cell histiocytosis, vasculitis |
Idiopathic pulmonary fibrosis (the commonest idiopathic ILD)
- Who: over 50 years, male, smokers; chronic, progressive fibrosis with usual interstitial pneumonia (UIP) pattern; unknown cause.
- Clinical: progressive dry cough and exertional breathlessness over months to years; fine "velcro" end-inspiratory crackles at the bases, finger clubbing; late: cyanosis and cor pulmonale.
- HRCT: subpleural, basal, reticular opacities with honeycombing and traction bronchiectasis (diagnostic without biopsy in the right clinical setting).
- Treatment: antifibrotics (nintedanib, pirfenidone) slow decline; oxygen, pulmonary rehabilitation, treat reflux and cough, vaccinations; lung transplant in selected patients; palliative care. Steroids do not help (and can harm) in IPF.
- Prognosis: poor; median survival about 3–5 years from diagnosis; acute exacerbations are often fatal.
Other important ILDs
- Sarcoidosis: non-caseating granulomas; young adults; bilateral hilar lymphadenopathy with or without parenchymal disease; erythema nodosum, arthralgia, uveitis, hypercalcaemia, raised ACE; Löfgren syndrome (bilateral hilar nodes + erythema nodosum + arthralgia, good prognosis). Treat with steroids if symptomatic or organ-threatening. In Kenya, TB is the main differential.
- Hypersensitivity pneumonitis: immune reaction to inhaled organic antigens (mouldy hay: farmer's lung; birds: bird fancier's lung); acute (flu-like 4–8 hours after exposure) or chronic fibrosis. Remove the exposure; steroids.
- CTD-ILD: commonly systemic sclerosis (NSIP), rheumatoid arthritis (UIP); treat with immunosuppression.
- Drug-induced: stop the drug; steroids if severe.
- Cryptogenic organising pneumonia: subacute, patchy consolidation not responding to antibiotics; excellent response to steroids.
Clinical approach
- History: onset and course, occupation and hobbies (birds, mould, dusts), drugs, smoking, family history, symptoms of CTD (joint pain, Raynaud's, rash, dry eyes), previous radiation or TB.
- Examination: clubbing, fine bibasal crackles, skin or joint signs of CTD, signs of pulmonary hypertension and right heart failure.
Investigations
- Chest X-ray: reticular or reticulonodular shadowing, reduced lung volumes, honeycombing; may be normal early.
- HRCT chest: the key test (UIP pattern, NSIP pattern, nodules, ground glass).
- Lung function: restrictive pattern: reduced FVC, FEV1/FVC normal or raised, reduced TLC and DLCO (transfer factor).
- ABG/oximetry: hypoxaemia, desaturation on exercise (6-minute walk test).
- Blood tests: FBC, ESR/CRP, ANA, RF, anti-CCP, ENA, ANCA, myositis panel, ACE and calcium (sarcoid), precipitins.
- Bronchoalveolar lavage (lymphocytosis in sarcoid and hypersensitivity pneumonitis), transbronchial or surgical lung biopsy when HRCT is not diagnostic.
- Echocardiography for pulmonary hypertension; HIV and TB screening in Kenya.
Management principles
- Remove the cause: stop the drug, avoid the antigen, treat the underlying CTD.
- Inflammatory ILD (NSIP, COP, sarcoid, HP, CTD-ILD): corticosteroids and steroid-sparing agents (azathioprine, mycophenolate, methotrexate, rituximab).
- IPF: antifibrotics; avoid steroids.
- Supportive: oxygen (resting or exertional hypoxaemia), pulmonary rehabilitation, vaccines (influenza, pneumococcal, COVID-19), stop smoking, treat reflux, cough and pulmonary hypertension.
- Lung transplantation referral; palliative care early.
Complications
- Respiratory failure, pulmonary hypertension and cor pulmonale, acute exacerbation, lung cancer (IPF raises the risk), pneumothorax, infection (PCP on immunosuppression), weight loss.
Exam points
- Dry cough + exertional dyspnoea + fine "velcro" crackles + clubbing = think IPF.
- HRCT is the key investigation; restrictive pattern with reduced DLCO on lung function.
- Ask about drugs and occupation.
- Sarcoid: bilateral hilar lymphadenopathy; non-caseating granulomas.
- IPF treatment: antifibrotics, not steroids.
Pharmacology at a glance
Tap a drug name for its full card (how it works, adverse effects, cautions, dose), then use Back to this note to return to this spot. Condition guide: idiopathic pulmonary fibrosis drugs.
| Drug | Class | Role here | Watch for |
|---|---|---|---|
| Nintedanib | Tyrosine kinase inhibitor (antifibrotic) | IPF and other progressive fibrosing ILD | Diarrhoea, liver tests, bleeding |
| Pirfenidone | Antifibrotic | IPF | Nausea, photosensitivity rash |
| Prednisolone | Systemic corticosteroid | Inflammatory ILD (sarcoid, organising pneumonia, hypersensitivity pneumonitis); not for IPF | High glucose, infection, bone loss |
| Methotrexate | Antimetabolite | Steroid-sparing agent in CTD-ILD, but can itself cause pneumonitis | Lung toxicity, liver, blood count |
| Rituximab | Anti-CD20 antibody | Refractory connective-tissue-disease ILD | Infusion reactions, infection |
| Amiodarone | Antiarrhythmic | A common drug cause of pulmonary fibrosis | Thyroid, liver, lung and eye toxicity |
| Nitrofurantoin | Urinary antibiotic | Drug cause of acute and chronic lung disease | Pulmonary reactions with long use |
| Bleomycin | Cytotoxic antibiotic | Chemotherapy cause of pulmonary fibrosis | Dose-related lung toxicity |
Always ask about drugs: stopping the cause is the first treatment in drug-induced lung disease.
Practice questions
1. A 65-year-old man has 18 months of dry cough and breathlessness, clubbing and bibasal fine end-inspiratory crackles. HRCT shows subpleural basal honeycombing. The treatment that slows progression is: A. Prednisolone · B. Nintedanib or pirfenidone · C. Antibiotics · D. Salbutamol · E. Methotrexate Answer: B.
2. The pattern of lung function in ILD is: A. Obstructive with high TLC · B. Restrictive with reduced DLCO · C. Normal · D. Isolated high FEV1/FVC with high TLC · E. Obstructive with raised DLCO Answer: B.
3. A young woman has erythema nodosum, arthralgia and bilateral hilar lymphadenopathy. The most likely diagnosis is: A. Tuberculosis · B. Lymphoma · C. Sarcoidosis (Löfgren syndrome) · D. IPF · E. Silicosis Answer: C.