CTICasesChronic Hypersensitivity Pneumonitis vs UIP — Value of Expiratory Imaging
Imaging findings
CT in a patient referred with a diagnosis of IPF demonstrates basal peripheral reticulation, ground-glass opacity, and areas of low attenuation that could represent early honeycomb cysts, with minimal traction bronchiectasis and some central involvement. On inspiratory imaging alone, a possible UIP pattern is suggested. Expiratory CT performed as three-level dynamic expirations reveals extensive air trapping in multiple lobes, confirming small airway involvement. Biopsy shows multiple granulomas consistent with chronic hypersensitivity pneumonitis rather than UIP/IPF.
Key takeaways
Chronic hypersensitivity pneumonitis can closely mimic UIP/IPF on inspiratory CT, particularly when it presents with basal peripheral reticulation and lacks the obvious mosaic attenuation of the subacute form. Expiratory CT imaging revealing extensive air trapping is a critical distinguishing feature that supports HP over UIP, as air trapping in HP results from small airway involvement. Granulomas on biopsy confirm the HP diagnosis but may be absent in end-stage fibrosing HP. Female sex and the presence of air trapping should lower the threshold for expiratory imaging and bronchoscopic or surgical biopsy before accepting a diagnosis of IPF.
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