A 41-year-old non-smoker woman presents with progressive dyspnoea, dry cough, and HRCT showing bilateral basal predominant reticulation, honeycombing with traction bronchiectasis, and subpleural distribution — no ground-glass opacity. What is the most likely diagnosis and what is the most reliable diagnostic feature on HRCT?

• A Nonspecific Interstitial Pneumonia (NSIP); ground-glass opacity predominance
• B Usual Interstitial Pneumonia (UIP) pattern; honeycombing with basal subpleural distribution ✓
• C Cryptogenic Organising Pneumonia (COP); peribronchial consolidation
• D Hypersensitivity Pneumonitis; upper lobe predominance with centrilobular nodules

Explanation

The UIP (usual interstitial pneumonia) pattern on HRCT — bilateral, basal-predominant, subpleural reticulation with honeycombing ± traction bronchiectasis — is the hallmark of idiopathic pulmonary fibrosis (IPF). Honeycombing in this distribution is the most specific HRCT feature of UIP and allows diagnosis of IPF without surgical biopsy when other causes are excluded. NSIP shows predominant ground-glass opacity. COP shows peribronchial consolidation. HP shows upper lobe centrilobular nodules, air trapping, and fibrosis without honeycombing predominantly.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.