A 62-year-old never-smoker woman presents with progressive dyspnea. HRCT shows bilateral basal-predominant subpleural honeycomb changes with traction bronchiectasis. No ground-glass opacity. Surgical biopsy shows temporal heterogeneity, fibroblastic foci adjacent to dense fibrosis, and no granulomas or significant inflammation. Which diagnosis and pattern does this represent, and what is the key molecular driver?

• A Nonspecific interstitial pneumonia (NSIP) pattern — associated with autoimmune disease; responds well to immunosuppression
• B Organizing pneumonia (OP) pattern — Masson body formation is the hallmark; excellent response to steroids
• C Usual interstitial pneumonia (UIP) pattern — the histological correlate of IPF; the key molecular driver is epithelial-mesenchymal transition (EMT) initiated by TGF-β1-mediated activation of alveolar type II (AEC2) cells, generating activated fibroblasts and myofibroblasts in the subpleural zones ✓
• D Respiratory bronchiolitis-ILD (RB-ILD) pattern — invariably associated with smoking; pigmented macrophages dominate

Explanation

The combination of basal subpleural honeycombing, traction bronchiectasis, minimal ground-glass opacity, temporal heterogeneity (areas of normal lung adjacent to dense fibrosis), and fibroblastic foci is pathognomonic for the UIP pattern, the histological substrate of idiopathic pulmonary fibrosis (IPF). Key pathomechanism: repetitive alveolar epithelial injury causes alveolar type II cell (AEC2) senescence and abnormal regeneration; damaged AEC2 cells secrete TGF-β1 and other profibrotic mediators that activate fibroblasts/myofibroblasts in subpleural zones, creating fibroblastic foci that evolve into dense fibrosis and honeycomb change. Nintedanib and pirfenidone target this pathway. NSIP shows temporal homogeneity and responds to steroids. OP shows Masson bodies and responds to steroids. RB-ILD is smoking-related.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.