Hypersensitivity pneumonitis

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Hypersensitivity pneumonitis
Diagnosis in short

Hypersensitivity pneumonitis. Trichrome stain.

Synonyms extrinsic allergic alveolitis

LM centrilobular prominence of lesions, granulomata, chronic interstitial inflammation consisting primarily of lymphocytes, interstitial fibrosis, air space involvement (alveolitis)
LM DDx usual interstitial pneumonia, asbestosis
Site lung - see diffuse lung diseases

Clinical history allergen exposure
Prevalence uncommon
Radiology upper lung predominant
Prognosis usu. good if allergen exposure eliminated
Clin. DDx other diffuse lung diseases, esp. idiopathic pulmonary fibrosis
Treatment eliminate allergen exposure

Hypersensitivity pneumonitis, abbreviated HP, is a diffuse lung diseases caused by an allergen.

It is also known as extrinsic allergic alveolitis, abbreviated EAA.


Specific diseases/etiology

Selected causes of hypersensitivity pneumonitis:[3]

Disease Cause
Silicosis silica exposure
Asbestosis asbestos
Flavour-worker's lung (popcorn lung) diacetyl - used for butter flavour[4]
Sick building syndrome volatile organic compounds, smoke, dampness
Berylliosis beryllium
Coal worker’s pneumoconiosis coal dust


  • Peripheral or peribronchiolar.[5]
    • Not large airways.



  • Lesions have centrilobular prominence - important feature. [6]
    • Allergens enter lung through airway which has a centrilobular location.
  • Granulomata (not typically seen in UIP) - important feature.[6]
  • Chronic interstitial inflammation consisting primarily of lymphocytes.
  • Interstitial fibrosis.
  • Air space involvement (alveolitis).



See also


  1. Kaltreider, HB. (Nov 1993). "Hypersensitivity pneumonitis.". West J Med 159 (5): 570-8. PMID 8279154. http://www.ncbi.nlm.nih.gov/pmc/articles/pmid/8279154/?tool=pubmed.
  2. URL: http://library.med.utah.edu/WebPath/EXAM/IMGQUIZ/pufrm.html. Accessed on: 4 December 2011.
  3. Zacharisen MC, Fink JN (November 2011). "Hypersensitivity pneumonitis and related conditions in the work environment". Immunol Allergy Clin North Am 31 (4): 769–86, vii. doi:10.1016/j.iac.2011.07.004. PMID 21978856.
  4. Egilman DS, Schilling JH, Menendez L (2011). "A proposal for a safe exposure level for diacetyl". Int J Occup Environ Health 17 (2): 122–34. PMID 21618944.
  5. Churg, A.; Muller, NL.; Flint, J.; Wright, JL. (Feb 2006). "Chronic hypersensitivity pneumonitis.". Am J Surg Pathol 30 (2): 201-8. PMID 16434894.
  6. 6.0 6.1 Ohtani, Y.; Saiki, S.; Kitaichi, M.; Usui, Y.; Inase, N.; Costabel, U.; Yoshizawa, Y. (Aug 2005). "Chronic bird fancier's lung: histopathological and clinical correlation. An application of the 2002 ATS/ERS consensus classification of the idiopathic interstitial pneumonias.". Thorax 60 (8): 665-71. doi:10.1136/thx.2004.027326. PMID 16061708.