Interstitial Lung Diseases and Occupational/Environmental Lung Disease
Domain 5 - Interstitial and Occupational Lung Disease
This domain tests pattern recognition on HRCT, multidisciplinary diagnosis, and exposure history. The Board expects you to distinguish idiopathic pulmonary fibrosis from hypersensitivity pneumonitis, sarcoidosis and occupational pneumoconioses, and to know when immunosuppression is harmful.
Core rules
- IPF is a chronic fibrosing ILD of unknown cause with a usual interstitial pneumonia pattern: honeycombing, traction bronchiectasis, basal and peripheral reticulation. Diagnosis is made by multidisciplinary team review; surgical biopsy is not required when the CT pattern is definite UIP.
- Antifibrotics, pirfenidone or nintedanib, slow FVC decline in IPF and progressive fibrosing ILD. They do not reverse fibrosis. Immunosuppression with prednisone plus azathioprine is harmful in IPF.
- Hypersensitivity pneumonitis requires exposure history, antigen testing when available, lymphocytosis on BAL, and centrilobular nodules or air trapping on HRCT. Avoid the antigen; steroids are used for significant physiologic impairment.
- Sarcoidosis: non-caseating granulomas, bilateral hilar lymphadenopathy, erythema nodosum, uveitis. Treatment is reserved for progressive pulmonary, cardiac, neurological or ocular disease.
- Occupational disease: silicosis (upper-lobe nodules, eggshell calcification, risk of TB), asbestosis (lower-lobe fibrosis, pleural plaques, mesothelioma risk), berylliosis (granulomatous), and byssinosis (cotton dust).
Worked example
A 68-year-old man has progressive dyspnoea, bibasal crackles and clubbing. HRCT shows subpleural honeycombing and traction bronchiectasis at the bases. There is no exposure history or connective tissue disease. This is a definite UIP pattern, and multidisciplinary review diagnoses IPF without lung biopsy. Start nintedanib or pirfenidone, offer pulmonary rehabilitation, vaccinate, and assess for oxygen and transplant. Do not start oral corticosteroids.
Traps that cost marks
- Calling any basal fibrosis IPF without excluding hypersensitivity pneumonitis, connective tissue disease and drug toxicity.
- Missing an occupational exposure history; ask about stone cutting, sandblasting, asbestos and farming.
- Treating IPF with steroids or immunosuppressants.
- Diagnosing sarcoidosis from hilar nodes alone without considering lymphoma or TB.
- Forgetting that silicosis increases tuberculosis risk.
Key points
- UIP on HRCT: honeycombing, traction bronchiectasis, basal-peripheral fibrosis.
- IPF diagnosis is multidisciplinary; typical UIP does not need biopsy.
- Antifibrotics slow decline; steroids are harmful in IPF.
- Hypersensitivity pneumonitis: exposure, BAL lymphocytosis, centrilobular nodules.
- Silicosis: upper-lobe nodules, eggshell calcification, TB risk.