A 45-year-old pigeon breeder has 6 months of progressive dyspnea and dry cough, worse on days he cleans the loft. HRCT shows diffuse centrilobular ground-glass nodules with mosaic attenuation and lobular air trapping. BAL shows 45% lymphocytes with a CD4:CD8 ratio below 1. What is the most likely diagnosis?
- A Idiopathic pulmonary fibrosis
- B Sarcoidosis
- C Chronic hypersensitivity pneumonitis ✓
- D Nonspecific interstitial pneumonia
Correct answer: C. Chronic hypersensitivity pneumonitis
Explanation
Antigen exposure history (pigeon proteins), inspiratory crackles, HRCT with centrilobular nodules, mosaic attenuation and air trapping, and BAL lymphocytosis exceeding 30% with inverted CD4:CD8 ratio establish chronic hypersensitivity pneumonitis. IPF shows subpleural basal honeycombing without air trapping and has a paucicellular BAL. NSIP lacks the three-density pattern, and sarcoidosis typically raises the CD4:CD8 ratio above 3.5.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.