Diffuse lung diseases

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Diffuse lung diseases, abbreviated DLD, are a group of uncommon pathologies, also known as idiopathic interstitial pneumonias, abbreviated IIPs, and interstitial lung disease, abbreviated ILD.

They are a subgroup of the medical lung diseases.

Diffuse lung disease is the preferred term, as some diseases lumped into this group have involvement of the alveoli, i.e. are not interstitial. Also, some DLDs are not considered idiopathic, e.g. DIP is caused by smoking.

An introduction to pulmonary pathology is found in the pulmonary pathology article.



  • Diffuse lung disease is best assessed on an open biopsy.
    • These procedure are quite invasive; thus, not infrequently clinicians will try a transbrochial biopsy that ends-up providing in useful information.

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The clinical findings are noted. The size and type of biopsy significantly limit the 
interpretation.  Suspected diffuse lung disease (interstitial lung disease) 
is best assessed on an open lung biopsy.


The sections show small fragments of lung parenchyma. A very small amount of anthracotic pigment is present. Interstitial fibrosis is not apparent. No granulomata are identified. No nuclear atypia is identified. Air-space macrophages show minimal pigmentation and are not present in large numbers. No significant airspace or interstitial inflammation is identified.

Histologic classification

Idiopathic interstitial pneumonia can be subclassified based on histologic appearance into the following patterns:[4][5]

Histology Clinical Correlates Associations
Desquamative interstitial pneumonia (DIP) DIP smoking
Diffuse alveolar damage (DAD) ARDS, AIP, TRALI ARDS: trauma, infection; TRALI: blood transfusion; AIP: viral (???)
Nonspecific interstitial pneumonia (NSIP) NSIP ???
Respiratory bronchiolitis RB-ILD smoking
Usual interstitial pneumonia (UIP) CVD, IPF, drug toxicity, pneumoconiosis allergen (hypersensitivity pneumonitis), idiopathic, autoimmune
Organizing pneumonia Cryptogenic organizing pneumonia autoimmune (???)
Lymphocytic interstitial pneumonia (LIP) LIP viral/autoimmune

ARDS = adult respiratory distress syndrome, AIP = acute interstitial pneumonia, TRALI = transfusion related acute lung injury, CVD = collagen vascular disease, IPF = idiopathic pulmonary fibrosis.


  • Usual interstitial pneumonia is the most common type of ILD.[6]

Gross pathologic DDx by location

Causes of upper lung fibrosis FASSTEN:[7]

Causes of lower lung fibrosis BAD RASH:[7]


Specific diseases/pattterns

Diffuse alveolar damage

  • Abbreviated DAD.

Usual interstitial pneumonia

  • Abbreviated UIP.


Non-specific interstitial pneumonia

  • Abbreviated NSIP.

Organizing pneumonia

Hypersensitivity pneumonitis

  • AKA extrinsic allergic alveolitis

Lymphocytic interstitial pneumonia

  • Often abbreviated LIP.

Respiratory bronchiolitis-interstitial lung disease

  • Abbreviated RB-ILD or RBILD.
  • AKA respiratory bronchiolitis-associated interstitial lung disease.

Desquamative interstitial pneumonia

  • Abbreviated DIP.

See also


  1. Nicholson AG (November 2002). "Classification of idiopathic interstitial pneumonias: making sense of the alphabet soup". Histopathology 41 (5): 381-91. PMID 12405906. http://www3.interscience.wiley.com/resolve/openurl?genre=article&sid=nlm:pubmed&issn=0309-0167&date=2002&volume=41&issue=5&spage=381.
  2. Flaherty KR, King TE, Raghu G, et al (October 2004). "Idiopathic interstitial pneumonia: what is the effect of a multidisciplinary approach to diagnosis?". Am. J. Respir. Crit. Care Med. 170 (8): 904-10. doi:10.1164/rccm.200402-147OC. PMID 15256390. http://ajrccm.atsjournals.org/cgi/pmidlookup?view=long&pmid=15256390.
  3. Kim DS, Collard HR, King TE (June 2006). "Classification and natural history of the idiopathic interstitial pneumonias". Proc Am Thorac Soc 3 (4): 285-92. doi:10.1513/pats.200601-005TK. PMID 16738191. http://pats.atsjournals.org/cgi/pmidlookup?view=long&pmid=16738191.
  4. Leslie KO, Wick MR. Practical Pulmonary Pathology: A Diagnostic Approach. Elsevier Inc. 2005. ISBN 978-0-443-06631-3.
  5. "American Thoracic Society/European Respiratory Society International Multidisciplinary Consensus Classification of the Idiopathic Interstitial Pneumonias. This joint statement of the American Thoracic Society (ATS), and the European Respiratory Society (ERS) was adopted by the ATS board of directors, June 2001 and by the ERS Executive Committee, June 2001". Am. J. Respir. Crit. Care Med. 165 (2): 277-304. January 2002. PMID 11790668. http://ajrccm.atsjournals.org/cgi/pmidlookup?view=long&pmid=11790668.
  6. Visscher DW, Myers JL (June 2006). "Histologic spectrum of idiopathic interstitial pneumonias". Proc Am Thorac Soc 3 (4): 322-9. doi:10.1513/pats.200602-019TK. PMID 16738196. http://pats.atsjournals.org/cgi/pmidlookup?view=long&pmid=16738196.
  7. 7.0 7.1 Yeung, J.C.; Leonard, Blair J. N. (2005). The Toronto Notes 2005 - Review for the MCCQE and Comprehensive Medical Reference (2005 ed.). The Toronto Notes Inc. for Medical Students Inc.. pp. R13. ISBN 978-0968592854.
  8. Humphrey, Peter A; Dehner, Louis P; Pfeifer, John D (2008). The Washington Manual of Surgical Pathology (1st ed.). Lippincott Williams & Wilkins. pp. 90. ISBN 978-0781765275.