Chronic hypersensitivity pneumonitis

Chronic hypersensitivity pneumonitis (CHP) refers to hypersensitivity pneumonitis where there is radiological evidence of fibrosis and represents the end-stage of repeated or persistent pneumonitis 7.

It is considered an immunopathological disorder occurring in susceptible individuals, where both humoral and cellular mechanisms are thought to participate in the development of lung lesions. 

High-resolution CT of the chest typically reveals indistinct centrilobular peribronchiolar nodular opacities - micronodules) of varying numbers 5. Other features include:

There is often a middle or upper zone predominance of CT findings with sparing of the lung bases, unlike non-specific interstitial pneumonia (NSIP) or usual interstitial pneumonia (UIP), which show a lower zone predominance.

The presence of an extensive reticular pattern, traction bronchiectasis, and honeycombing have been shown to closely correlate with the presence of histologic fibrosis in chronic hypersensitivity pneumonitis 6.

The presence of fibrotic changes confers a poor prognosis.

In some cases, it may be difficult to differentiate from idiopathic pulmonary fibrosis - UIP cases are also thought to have honeycombing and peripheral or lower lung zone predominance of disease, and less likely to have micronodules 4.


Article information

rID: 17191
System: Chest
Synonyms or Alternate Spellings:
  • Chronic hypersensitivity pneumonitis (CHP)
  • Chronic HP
  • Chronic EAA
  • Chronic extrinsic allergic alveolitis
  • Chronic extrinsic allergic alveolitis (EAA)

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Cases and figures

  • Case 1: secondary to pigeons
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  • Case 2: probable
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  • Case 3
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