Which histologic findings are characteristic of acute hypersensitivity pneumonitis (HP)?

Updated: Oct 08, 2020
  • Author: Caleb Hsieh, MD, MS; Chief Editor: John J Oppenheimer, MD  more...
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Because biopsy is generally not indicated, relatively little is known about the gross pathologic features of acute hypersensitivity pneumonitis. The most characteristic pathologic feature is neutrophilic interstitial infiltrate. Other features may include small-vessel vasculitis with immunoglobulin and complement deposition, diffuse alveolar damage, and/or intraalveolar fibrin accumulation. [10] Note the image below.

Light microscopy shows mononuclear infiltration an Light microscopy shows mononuclear infiltration and noncaseating granulomas usually observed in association with acute hypersensitivity pneumonitis, but it also can be observed in subacute and chronic disease.

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