A 46-year-man who keeps pigeons has 6 months of progressive breathlessness and a 4 kg weight loss. Examination shows mid-inspiratory squeaks. HRCT demonstrates diffuse centrilobular ground-glass nodules with mosaic attenuation and lobular air trapping on expiratory images; there is no honeycombing. Total lung capacity is mildly reduced and BAL shows lymphocytosis of 45%. What is the diagnosis?

• A Subacute hypersensitivity pneumonitis ✓
• B Idiopathic pulmonary fibrosis with usual interstitial pneumonia pattern
• C Sarcoidosis stage II
• D Desquamative interstitial pneumonia

Explanation

Avian antigen exposure, inspiratory squeaks, centrilobular ground-glass nodules, three-density mosaic attenuation with lobular air trapping, and BAL lymphocytosis together establish subacute hypersensitivity pneumonitis, formerly called bird fancier lung. UIP/IPF requires basal subpleural honeycombing without air trapping, sarcoidosis features hilar nodes and perilymphatic nodules, and DIP occurs in smokers with macrophage-rich BAL fluid rather than lymphocytosis.

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

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Written and medically reviewed by the StethoPrep medical team.