Extrinsic Allergic Alveolitis

Extrinsic Allergic Alveolitis

Hypersensitivity pneumonitis shows the 2 most important features for its diagnosis: Areas of bronchiolitis obliterans image and the presence of ill-defined granulomas image.

In other areas of lung parenchyma, there is a discrete presence of numerous noncaseating granulomas image. The presence of ill-defined granulomas is characteristic of HP.



  • Hypersensitivity pneumonitis (HP)


  • Granulomatous lung disease secondary to inhalation of organic antigens or chemicals


Environmental Exposure

  • History of exposure to organic antigens

    • Saccharopolyspora rectivirgula in “farmer’s lung” (moldy hay)

    • Thermoactinomyces sacchari in bagassosis (sugar cane workers)

    • Animal protein from bird feathers and feces from birds


  • HP represents immune complex-mediated (type III) T-cell and delayed (type IV) hypersensitivity reaction



  • Incidence

    • Exact incidence of HP is unknown

      • However, HP may be more prevalent in people exposed to birds

  • Age

    • Usually in adults

  • Gender

    • No predilection for any particular gender

  • Ethnicity

    • No predilection for any particular ethnic group


  • Lung without predilection for specific side or lung segment


  • Cough

  • Dyspnea

  • Fever

  • Chills

  • Wheezing

  • Malaise

Laboratory Tests

  • Pulmonary function tests may be abnormal

  • Erythrosedimentation may be elevated

  • C-protein may be elevated

Natural History

  • Acute hypersensitivity pneumonitis

    • 4-6 hours after exposure to antigen

    • Episode may last 12-18 hours

  • Chronic hypersensitivity pneumonitis

    • Patients may have continuous exposure to antigen over months or years

    • Patients may not experience acute episode

    • This type eventually gets biopsied

Jul 9, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Extrinsic Allergic Alveolitis
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