Lung - nontumor
Extrinsic allergic alveolitis

Author: Elliot Weisenberg, M.D. (see Authors page)

Revised: 1 March 2017, last major update September 2011

Copyright: (c) 2003-2017,, Inc.

PubMed search: extrinsic allergic alveolitis [title]

Cite this page: Extrinsic allergic alveolitis. website. Accessed June 27th, 2017.
Definition / general
  • Also called hypersensitivity pneumonitis
  • Note: many agents cause disease, only most important are discussed
  • Spectrum of immunologically mediated, interstitial lung disorders caused by intense, often prolonged exposure to inhaled organic dusts and occupational antigens
  • Individuals have abnormal sensitivity or heightened reactivity to these antigens
  • Similar to asthma, but involves alveoli, not bronchi
  • Acute attacks occur 4 - 6 hours after inhalation; diffuse / nodular pulmonary infiltrates appear on chest Xray; chronic exposure causes shortness of breath, respiratory failure, cyanosis, decreased total lung capacity and compliance
  • Chronic low levels of exposure may cause diffuse interstitial lung disease with fibrosis and honeycomb lung
  • Good prognosis, responds well to steroids and withdrawal of offending antigen
  • May progress to chronic obstructive lung disease
  • Highest risk from dust due to carding and blending; less risk with less dusty operations such as weaving and spinning
  • In nonsmoking workers, changes mostly reversible upon cessation of dust exposure
  • Causes: spores of thermophilic bacteria, fungi, animal proteins, bacteria from hay, grain, sugar cane, bark, cheese, cork and animal feces; exposure results in early formation of type III immune complexes, then type IV delayed hypersensitivity
  • Air conditioner lung: due to thermophilic bacteria
  • Byssinosis: in textile workers due to fibers from cotton, linen and hemp; resembles asthma clinically; disease mechanism may not be immune mediated, endotoxin from bacterial contamination of cotton may play a role
  • Farmer's lung: from moldy hay containing spores of thermophilic actinomycetes
  • Maple bark stripper’s lung: fungal spores
  • Pigeon breeder's lung: also called bird fancier's disease; proteins from serum, feathers and excreta
  • Remove environmental agent early
Microscopic (histologic) description
  • Interstitial bronchiolocentric pneumonitis with lymphocytes, plasma cells and foamy macrophages also in alveolar space and terminal airways
  • Interstitial fibrosis, obliterative bronchiolitis, poorly circumscribed epithelioid granulomas and intra-alveolar exudate
  • Also nodules of organizing fibroblasts, histiocytes and other inflammatory cells
  • In byssinosis, hemosiderin coated strands of fiber within fibrous tissue known as byssinoisis bodies may be encountered
Microscopic (histologic) images

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