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| ==Hypersensitivity pneumonitis== | | ==Hypersensitivity pneumonitis== |
| *AKA ''extrinsic allergic alveolitis'' | | *AKA ''extrinsic allergic alveolitis'' |
| | | {{Main|Hypersensititivty pneumonitis}} |
| ===General===
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| *Exposure to stuffs... e.g. moldy hay - ''Farmer's lung'', atypical mycobacteria - ''hot tub lung''.
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| *Upper lung predominant disease.
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| **Mnemonic ''FASSTEN'' - upper lung field: [[Farmer's lung]], [[Ankylosing spondylitis]], [[Sarcoidosis]], [[Silicosis]], [[Tuberculosis]] (miliary), [[Eosinophilic granuloma]], [[Neurofibromatosis]].
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| *An immune complex-mediated [[hypersensitivity]]<ref name=pmid8279154>{{Cite journal | last1 = Kaltreider | first1 = HB. | title = Hypersensitivity pneumonitis. | journal = West J Med | volume = 159 | issue = 5 | pages = 570-8 | month = Nov | year = 1993 | doi = | PMID = 8279154 | url = http://www.ncbi.nlm.nih.gov/pmc/articles/pmid/8279154/?tool=pubmed }}</ref> (Gell-Coombs classification type III).
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| **If chronic, may develop into a cell-mediated hypersensitivity (Gell-Coombs classification type IV).<ref>URL: [http://library.med.utah.edu/WebPath/EXAM/IMGQUIZ/pufrm.html http://library.med.utah.edu/WebPath/EXAM/IMGQUIZ/pufrm.html]. Accessed on: 4 December 2011.</ref>
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| ===Microscopic===
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| Features:
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| * Lesions have centrilobular prominence - '''important feature'''. <ref name=pmid16061708/>
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| ** Allergens enter lung through airway which has a centrilobular location.
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| * [[Granulomata]] (not typically seen in UIP) - '''important feature'''.<ref name=pmid16061708>{{Cite journal | last1 = Ohtani | first1 = Y. | last2 = Saiki | first2 = S. | last3 = Kitaichi | first3 = M. | last4 = Usui | first4 = Y. | last5 = Inase | first5 = N. | last6 = Costabel | first6 = U. | last7 = Yoshizawa | first7 = Y. | title = Chronic bird fancier's lung: histopathological and clinical correlation. An application of the 2002 ATS/ERS consensus classification of the idiopathic interstitial pneumonias. | journal = Thorax | volume = 60 | issue = 8 | pages = 665-71 | month = Aug | year = 2005 | doi = 10.1136/thx.2004.027326 | PMID = 16061708 }}</ref>
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| * Chronic interstitial inflammation consisting primarily of lymphocytes.
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| * Interstitial fibrosis.
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| * Air space involvement (alveolitis).
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| DDx:
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| *[[Usual interstitial pneumonia]].
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| ====Images====
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| <gallery>
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| Image:Hypersensitivity_pneumonitis_low_mag.jpg | Hypersensitivity pneumonitis - low mag. (WC/Nephron)
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| Image:Hypersensitivity_pneumonitis_intermed_mag.jpg | Hypersensitivity pneumonitis - intermed. mag. (WC/Nephron)
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| Image:Hypersensitivity_pneumonitis_high_mag.jpg | Hypersensitivity pneumonitis - high mag. (WC/Nephron)
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| </gallery>
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| ==Lymphocytic interstitial pneumonia== | | ==Lymphocytic interstitial pneumonia== |