Interstitial Lung Disease: Pattern Recognition Before Biopsy
Two questions on every ILD case
The first is whether there is an identifiable cause: exposures (birds, mold, metal dusts, drugs such as amiodarone, methotrexate, nitrofurantoin), connective tissue disease, or sarcoidosis. The second is the HRCT pattern. Usual interstitial pneumonia shows peripheral, basal-predominant reticulation with honeycombing and traction bronchiectasis and minimal ground-glass. When UIP is definite on HRCT and no cause is found, the diagnosis is idiopathic pulmonary fibrosis (IPF) and a surgical biopsy is unnecessary and risky - this is a favorite exam trap.
Patterns and their associations
Nonspecific interstitial pneumonia shows bilateral ground-glass with fine reticulation, often in connective tissue disease or drug injury, and carries a better prognosis than UIP. Hypersensitivity pneumonitis classically shows upper-lobe ground-glass, centrilobular nodules, and air trapping on expiratory images, with antigen exposure at home or work. Sarcoidosis produces bilateral hilar lymphadenopathy and perilymphatic nodules, often upper-lobe, with noncaseating granulomas. Eosinophilic granulomatosis with polyangiitis, lymphangioleiomyomatosis, and pulmonary Langerhans cell histiocytosis are the less common names to recognize.
Physiology and management
Restriction means reduced TLC with preserved or increased FEV1/FVC; DLCO falls early and correlates with disease extent. Do not repeat a battery of serologies in a patient with classic IPF. Steroids and immunosuppression are beneficial in many inflammatory ILDs but harmful in IPF; antifibrotics (pirfenidone, nintedanib) slow decline and treat acute exacerbations poorly. Antigen avoidance is the core therapy for hypersensitivity pneumonitis. Lung transplantation referral should be considered early.
Worked rule
Peripheral-basal honeycombing plus no exposure or autoimmune serology = IPF; initiate antifibrotic, avoid steroids.