A 52-year-old dairy farmer has 6 months of progressive breathlessness with a dry cough. Examination reveals diffuse inspiratory squeaks. HRCT shows diffuse centrilobular ground-glass nodules, patchy mosaic attenuation, and marked air trapping on expiratory sequences. There is no subpleural honeycombing and pulmonary function shows a reduced DLCO with preserved lung volumes. What is the most likely diagnosis?

• A Usual interstitial pneumonia
• B Nonspecific interstitial pneumonia
• C Subacute hypersensitivity pneumonitis ✓
• D Pulmonary alveolar proteinosis

Explanation

Centrilobular ground-glass nodules, mosaic attenuation with air trapping on expiration, and exposure to organic dusts (mouldy hay in farmer's lung) define hypersensitivity pneumonitis. UIP shows basal subpleural honeycombing without air trapping, and NSIP shows uniform subpleural ground glass with volume loss rather than centrilobular nodules, which excludes those options. Alveolar proteinosis shows geographic crazy paving with lipoproteinaceous alveolar filling, not centrilobular nodules, and is not occupation-linked in this pattern.

Reference: Fishman's Pulmonary Diseases and Disorders, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.