A 52-year-old woman presents with progressive exertional dyspnoea, dry cough, bilateral basilar crackles, and clubbing. HRCT shows bilateral lower-lobe predominant honeycombing with traction bronchiectasis, minimal ground-glass opacity. Bronchoalveolar lavage shows 18% lymphocytes. Pulmonary function shows reduced TLC, reduced DLCO, and reduced FVC. The BAL lymphocytosis most likely indicates:
- A Hypersensitivity pneumonitis rather than IPF, as IPF characteristically shows neutrophilia/eosinophilia on BAL ✓
- B No diagnostic significance — BAL lymphocytosis is common in IPF
- C Sarcoidosis given the bilateral nature and restriction
- D Lymphangioleiomyomatosis — the primary differential in females with restriction
Correct answer: A. Hypersensitivity pneumonitis rather than IPF, as IPF characteristically shows neutrophilia/eosinophilia on BAL
Explanation
In a patient with UIP-pattern HRCT (honeycombing + traction bronchiectasis), BAL lymphocytosis > 20–30% suggests hypersensitivity pneumonitis (HP) as an alternative diagnosis, since IPF characteristically shows neutrophilia (± eosinophilia) on BAL with lymphocytes typically < 20%. Distinguishing HP with UIP pattern from IPF is clinically critical because HP may respond to antigen avoidance and immunosuppression whereas IPF does not. ATS/ERS 2020 HP guidelines include BAL lymphocytosis ≥ 30% as a key feature supporting HP diagnosis.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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