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Humidifier lung — SCE Respiratory MCQ

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HardOccupational lung diseaseHumidifier lungSCE Respiratory

A 54-year-old man develops fever, cough and breathlessness on Monday mornings after cleaning a contaminated humidifier at work. HRCT shows diffuse ground-glass nodules and mosaic attenuation; symptoms improve during holidays. BAL lymphocytes are elevated and serum precipitins to thermophilic actinomycetes are positive. Spirometry shows mild restriction. What is the most likely underlying cause?

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Correct answer: D — Antigen-driven immune reaction in hypersensitivity pneumonitis

The best answer is “Antigen-driven immune reaction in hypersensitivity pneumonitis”. The clinical pattern, physiology and imaging described are most consistent with Antigen-driven immune reaction in hypersensitivity pneumonitis. The competing diagnoses may share individual findings, but do not account for the complete combination in the stem. The remaining choices—“IgE-mediated occupational asthma, after specialist assessment”, “Direct carbon monoxide toxicity”, “Alpha-1 antitrypsin deficiency, after safety review”, “Surfactant accumulation from GM-CSF antibodies”—are credible in related respiratory presentations, but each addresses a different diagnostic, staging or management decision and does not fit the decisive findings and pathway position in this stem.

Reference: British Thoracic Society pulmonary nodule guideline: https://thorax.bmj.com/content/70/Suppl_2/ii1