Hypersensitivity pneumonitis

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[edit] Discussion

  • Hypersensitivity pneumonitis is also known as extrinsic allergic alveolitis
  • Inflammatory lung disease caused by inhalation of airborne organic particulate matter. These particles, which are usually 1-5 ┬Ám in diameter, deposit in distal air spaces and produce an immune-mediated inflammatory response in sensitized individuals.
  • Causative agents are numerous and include bacteria, fungi, avian proteins, and wood dusts.
  • Most exposures are occupational, but hobbies such as bird breeding are also implicated.
  • Most common and well-studied forms of hypersensitivity pneumonitis are farmer's lung and bird fancier's lung.
  • Treatment is:
    • Cessation of exposure to causative agent
    • Steroids

[edit] Imaging Findings

Acute hypersensitivity pneumonitis

  • Chest radiographs in affected patients may be normal; thin-section CT can be helpful in these patients for showing characteristic centrilobular ground glass or nodular opacities.
  • When abnormal, chest radiographs typically show focal or diffuse heterogeneous or homogeneous opacities.


Subacute hypersensitivity pneumonitis

  • Patients with subacute disease usually have a more indolent clinical presentation. Nodular opacities are a characteristic feature on chest radiographs and CT. Centrilobular ground-glass or nodular opacities on CT suggest the diagnosis.
  • Head cheese sign

Chronic hypersensitivity pneumonitis

  • Chronic disease typically manifests with upper lung zone fibrosis. Characteristic distribution and presence of centrilobular nodules on CT help distinguish chronic hypersensitivity pneumonitis from idiopathic pulmonary fibrosis.

[edit] Images

Patient #1: Patient who fancies birds presents with SOB

[edit] See Also

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