Bronchiolitis pathophysiology: Difference between revisions
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==Overview== | ==Overview== | ||
Bronchiolitis is transmitted by air droplets | Bronchiolitis is transmitted by air droplets if it is caused by [[Human respiratory syncytial virus|RSV]] and that leads to [[infection]] of [[nasopharyngeal]] [[mucosa]]. After the infection, the virus will spread to the lower airway tracts till it reaches the [[bronchioles]] where the [[viral replication]] takes place. The viral infection induces [[inflammation]] which leads to [[edema]] and [[necrosis]] of the bronchioles [[epithelium]]. [[Cough reflex]] occurs due to exposure of the subepithelial tissue and [[nerve fibers]]. [[Vascular]] permeablity increases leading to edema and [[swelling]]. Histopathologically, [[bronchiolitis obliterans]] shows [[intraluminal]] [[polyps]], [[inflammatory]] [[Infiltration (medical)|infiltration]] and [[macrophages]]. Constrictive bronchiolitis shows thickening of the airways and interluminal narrowing. | ||
==Pathophysiology== | ==Pathophysiology== | ||
===Transmission=== | ===Transmission=== | ||
*Bronchiolitis is transmitted between individuals by air droplets | *Bronchiolitis is not transmitted between individuals but when it is infected by RSV it may be transmitted by air droplets. | ||
*This air droplets lead to infection of the nasopharyngeal mucosa. | *This air droplets lead to infection of the nasopharyngeal mucosa. | ||
===Pathogenesis=== | ===Pathogenesis=== | ||
Bronchiolitis is caused through viral replication process and inflammation as the following:<ref name="pmid23102068">{{cite journal| author=Garibaldi BT, Illei P, Danoff SK| title=Bronchiolitis. | journal=Immunol Allergy Clin North Am | year= 2012 | volume= 32 | issue= 4 | pages= 601-19 | pmid=23102068 | doi=10.1016/j.iac.2012.08.002 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23102068 }} </ref> | Bronchiolitis is caused through viral replication process and inflammation as the following:<ref name="pmid23102068">{{cite journal| author=Garibaldi BT, Illei P, Danoff SK| title=Bronchiolitis. | journal=Immunol Allergy Clin North Am | year= 2012 | volume= 32 | issue= 4 | pages= 601-19 | pmid=23102068 | doi=10.1016/j.iac.2012.08.002 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=23102068 }} </ref> | ||
*Starting from the nasopharyngeal mucosa the RSV will spread to the lower airway tracts. It will spread till reaching the bronchioles where viral replication takes place. | *Starting from the nasopharyngeal mucosa the [[Human respiratory syncytial virus|RSV]] will spread to the lower airway tracts. It will spread till reaching the [[bronchioles]] where [[viral replication]] takes place. | ||
*The [[viral infection]] induces an [[inflammatory]] response which leads to infiltration of [[Inflamation#Celular component|inflammatory cells]] (RSV-specific lymphocytes), [[edema]] and [[necrosis]] of the [[epithelium]] in the [[bronchioles]] which is then sloughed into the lumina causing proliferation of cuboidal epithelial cells without cilia.<ref name="Mandell">{{Cite book | last1 = Mandell | first1 = Gerald L. | last2 = Bennett | first2 = John E. (John Eugene) | last3 = Dolin | first3 = Raphael. | title = Mandell, Douglas, and Bennett's principles and practice of infectious disease | date = 2010 | publisher = Churchill Livingstone/Elsevier | location = Philadelphia, PA | isbn = | pages = }}</ref><ref name="pmid19209271">{{cite journal| author=Wright M, Mullett CJ, Piedimonte G| title=Pharmacological management of acute bronchiolitis. | journal=Ther Clin Risk Manag | year= 2008 | volume= 4 | issue= 5 | pages= 895-903 | pmid=19209271 | doi= | pmc=PMC2621418 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19209271 }} </ref> | *The [[viral infection]] induces an [[inflammatory]] response which leads to infiltration of [[Inflamation#Celular component|inflammatory cells]] (RSV-specific lymphocytes), [[edema]] and [[necrosis]] of the [[epithelium]] in the [[bronchioles]] which is then sloughed into the lumina causing proliferation of cuboidal [[epithelial cells]] without [[cilia]].<ref name="Mandell">{{Cite book | last1 = Mandell | first1 = Gerald L. | last2 = Bennett | first2 = John E. (John Eugene) | last3 = Dolin | first3 = Raphael. | title = Mandell, Douglas, and Bennett's principles and practice of infectious disease | date = 2010 | publisher = Churchill Livingstone/Elsevier | location = Philadelphia, PA | isbn = | pages = }}</ref><ref name="pmid19209271">{{cite journal| author=Wright M, Mullett CJ, Piedimonte G| title=Pharmacological management of acute bronchiolitis. | journal=Ther Clin Risk Manag | year= 2008 | volume= 4 | issue= 5 | pages= 895-903 | pmid=19209271 | doi= | pmc=PMC2621418 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=19209271 }} </ref> | ||
*Virus causes lysis to the epithelial tissue which leads to the exposure of the | *[[Virus]] causes lysis to the epithelial tissue which leads to the exposure of the subepithelial tissue and nerve fibers so, [[cough reflex]] takes place. | ||
*The vascular permeability increases which result in edema and swelling. | *The vascular permeability increases which result in [[edema]] and swelling. | ||
*This inflammation process leads to complete or partial obstruction due to reduction of the bronchiolar lumina and [[Necrosis|necrotic tissue]] accumulation producing a valve mechanism, leading to hyperinflation. | *This [[inflammation]] process leads to complete or partial obstruction due to reduction of the bronchiolar lumina and [[Necrosis|necrotic tissue]] accumulation producing a [[valve]] mechanism, leading to hyperinflation. | ||
*By this mechanism, air can flow into the [[lungs]] by increased negative pressure during [[inspiration]] but is unable to flow out of the lung as the airway's diameter is smaller during [[expiration]].<ref name="Mandell">{{Cite book | last1 = Mandell | first1 = Gerald L. | last2 = Bennett | first2 = John E. (John Eugene) | last3 = Dolin | first3 = Raphael. | title = Mandell, Douglas, and Bennett's principles and practice of infectious disease | date = 2010 | publisher = Churchill Livingstone/Elsevier | location = Philadelphia, PA | isbn = | pages = }}</ref> Obstructed areas can evolve to [[atelectasis]]. In children, Kohn channels are not well developed, therefore [[atelectasis]] and hyperinflation can be greater. | *By this mechanism, air can flow into the [[lungs]] by increased negative pressure during [[inspiration]] but is unable to flow out of the lung as the airway's diameter is smaller during [[expiration]].<ref name="Mandell">{{Cite book | last1 = Mandell | first1 = Gerald L. | last2 = Bennett | first2 = John E. (John Eugene) | last3 = Dolin | first3 = Raphael. | title = Mandell, Douglas, and Bennett's principles and practice of infectious disease | date = 2010 | publisher = Churchill Livingstone/Elsevier | location = Philadelphia, PA | isbn = | pages = }}</ref> Obstructed areas can evolve to [[atelectasis]]. In children, Kohn channels are not well developed, therefore [[atelectasis]] and hyperinflation can be greater. | ||
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Bronchiolitis shows histopathological findings that differ between different types of the bronchiolitis.<ref name="pmid16088569">{{cite journal| author=Couture C, Colby TV| title=Histopathology of bronchiolar disorders. | journal=Semin Respir Crit Care Med | year= 2003 | volume= 24 | issue= 5 | pages= 489-98 | pmid=16088569 | doi=10.1055/s-2004-815600 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=16088569 }} </ref> | Bronchiolitis shows histopathological findings that differ between different types of the bronchiolitis.<ref name="pmid16088569">{{cite journal| author=Couture C, Colby TV| title=Histopathology of bronchiolar disorders. | journal=Semin Respir Crit Care Med | year= 2003 | volume= 24 | issue= 5 | pages= 489-98 | pmid=16088569 | doi=10.1055/s-2004-815600 | pmc= | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=16088569 }} </ref> | ||
*Bronchiolitis obliterans: | *Bronchiolitis obliterans: | ||
**Intraluminal polyps which are protrusions inside the bronchioles with fibroblastic proliferation within it. | **Intraluminal [[polyps]] which are protrusions inside the [[bronchioles]] with [[fibroblastic]] [[proliferation]] within it. | ||
**Inflammatory infiltration | **Inflammatory [[Infiltration (medical)|infiltration]] | ||
**Type two pneumocytes lining the alveoli | **Type two [[pneumocytes]] lining the [[alveoli]] | ||
**Macrophages | **[[Macrophages]] | ||
*Constrictive bronchiolitis: | *Constrictive bronchiolitis: | ||
**Scars leading to interluminal narrowing and obstruction | **[[Scar|Scars]] leading to interluminal narrowing and [[obstruction]] | ||
**Thickening of the airways due to submucosal collagen and fibrosis | **Thickening of the airways due to [[submucosal]] [[collagen]] and [[fibrosis]] | ||
*Proliferative bronchiolitis: | *Proliferative bronchiolitis: | ||
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Alonso Alvarado, M.D. [2]
Overview
Bronchiolitis is transmitted by air droplets if it is caused by RSV and that leads to infection of nasopharyngeal mucosa. After the infection, the virus will spread to the lower airway tracts till it reaches the bronchioles where the viral replication takes place. The viral infection induces inflammation which leads to edema and necrosis of the bronchioles epithelium. Cough reflex occurs due to exposure of the subepithelial tissue and nerve fibers. Vascular permeablity increases leading to edema and swelling. Histopathologically, bronchiolitis obliterans shows intraluminal polyps, inflammatory infiltration and macrophages. Constrictive bronchiolitis shows thickening of the airways and interluminal narrowing.
Pathophysiology
Transmission
- Bronchiolitis is not transmitted between individuals but when it is infected by RSV it may be transmitted by air droplets.
- This air droplets lead to infection of the nasopharyngeal mucosa.
Pathogenesis
Bronchiolitis is caused through viral replication process and inflammation as the following:[1]
- Starting from the nasopharyngeal mucosa the RSV will spread to the lower airway tracts. It will spread till reaching the bronchioles where viral replication takes place.
- The viral infection induces an inflammatory response which leads to infiltration of inflammatory cells (RSV-specific lymphocytes), edema and necrosis of the epithelium in the bronchioles which is then sloughed into the lumina causing proliferation of cuboidal epithelial cells without cilia.[2][3]
- Virus causes lysis to the epithelial tissue which leads to the exposure of the subepithelial tissue and nerve fibers so, cough reflex takes place.
- The vascular permeability increases which result in edema and swelling.
- This inflammation process leads to complete or partial obstruction due to reduction of the bronchiolar lumina and necrotic tissue accumulation producing a valve mechanism, leading to hyperinflation.
- By this mechanism, air can flow into the lungs by increased negative pressure during inspiration but is unable to flow out of the lung as the airway's diameter is smaller during expiration.[2] Obstructed areas can evolve to atelectasis. In children, Kohn channels are not well developed, therefore atelectasis and hyperinflation can be greater.
Histopathology
Bronchiolitis shows histopathological findings that differ between different types of the bronchiolitis.[4]
- Bronchiolitis obliterans:
- Intraluminal polyps which are protrusions inside the bronchioles with fibroblastic proliferation within it.
- Inflammatory infiltration
- Type two pneumocytes lining the alveoli
- Macrophages
- Constrictive bronchiolitis:
- Scars leading to interluminal narrowing and obstruction
- Thickening of the airways due to submucosal collagen and fibrosis
- Proliferative bronchiolitis:
- Histopathology shows Masson bodies which are fibrotic buds extend to the alveoli.
References
- ↑ Garibaldi BT, Illei P, Danoff SK (2012). "Bronchiolitis". Immunol Allergy Clin North Am. 32 (4): 601–19. doi:10.1016/j.iac.2012.08.002. PMID 23102068.
- ↑ 2.0 2.1 Mandell, Gerald L.; Bennett, John E. (John Eugene); Dolin, Raphael. (2010). Mandell, Douglas, and Bennett's principles and practice of infectious disease. Philadelphia, PA: Churchill Livingstone/Elsevier.
- ↑ Wright M, Mullett CJ, Piedimonte G (2008). "Pharmacological management of acute bronchiolitis". Ther Clin Risk Manag. 4 (5): 895–903. PMC 2621418. PMID 19209271.
- ↑ Couture C, Colby TV (2003). "Histopathology of bronchiolar disorders". Semin Respir Crit Care Med. 24 (5): 489–98. doi:10.1055/s-2004-815600. PMID 16088569.