Clinical meaning
Interstitial lung diseases (ILDs) are a heterogeneous group of disorders characterized by inflammation and/or fibrosis of the lung parenchyma. Idiopathic pulmonary fibrosis (IPF) is the most common and most severe ILD, characterized by usual interstitial pneumonia (UIP) pattern: patchy, peripheral, basal-predominant fibrosis with honeycombing and fibroblastic foci. The pathogenesis involves repetitive alveolar epithelial cell injury triggering aberrant wound healing — activated myofibroblasts deposit excessive extracellular matrix (collagen) causing progressive, irreversible scarring. Other ILDs include connective tissue disease-associated (CTD-ILD — especially SSc, RA, myositis), hypersensitivity pneumonitis (HP — from organic antigen exposure: bird proteins, mold, chemicals), sarcoidosis, drug-induced ILD, and pneumoconioses (asbestosis, silicosis). HRCT pattern recognition (UIP vs NSIP vs organizing pneumonia) guides diagnosis and management. PFTs show restrictive pattern with reduced DLCO, which is often the earliest abnormality.
Diagnosis & workup
Diagnostics & workup: - HRCT: pattern recognition — UIP (honeycombing, traction bronchiectasis, basal-predominant), NSIP (ground-glass predominant, basal), HP (upper/mid-zone predominance, air trapping, mosaic attenuation) - PFTs: restrictive pattern (reduced TLC, FVC) with reduced DLCO — DLCO < 40% predicted carries poor prognosis - 6MWT with SpO2 monitoring: exercise desaturation (> 4% drop) suggests significant disease; distance correlates with prognosis - Autoimmune serologies: ANA, anti-CCP, RF, anti-Jo-1, anti-Scl-70, myositis panel (for CTD-ILD screening) - Serum precipitins (IgG) to specific antigens for HP (bird, mold panels) - BAL: lymphocytosis (HP, sarcoidosis, NSIP), eosinophilia (drug-induced, eosinophilic pneumonia), neutrophilia (IPF — poor prognosis) - Surgical lung biopsy (VATS): gold standard when HRCT pattern is indeterminate; establishes histological pattern - Multidisciplinary discussion (MDD): pulmonology + radiology + pathology — current gold standard for ILD diagnosis