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**[[Immunity (medical)|Immune]] activation due to GI [[infection]] also increases [[Enteroendocrine cells|enteroendocrine]] cells, calprotectin-positive [[Macrophage|macrophages]], [[Intraepithelial lymphocyte|intraepithelial]] [[Lymphocyte|lymphocytes]], and l[[Lamina propria|amina propria]] [[T cell|T cells]] which contribute directly to [[abdominal pain]] perception. <ref name="pmid20101257">{{cite journal |vauthors=Ohman L, Simrén M |title=Pathogenesis of IBS: role of inflammation, immunity and neuroimmune interactions |journal=Nat Rev Gastroenterol Hepatol |volume=7 |issue=3 |pages=163–73 |year=2010 |pmid=20101257 |doi=10.1038/nrgastro.2010.4 |url=}}</ref><ref name="pmid22730468">{{cite journal |vauthors=Simrén M, Barbara G, Flint HJ, Spiegel BM, Spiller RC, Vanner S, Verdu EF, Whorwell PJ, Zoetendal EG |title=Intestinal microbiota in functional bowel disorders: a Rome foundation report |journal=Gut |volume=62 |issue=1 |pages=159–76 |year=2013 |pmid=22730468 |pmc=3551212 |doi=10.1136/gutjnl-2012-302167 |url=}}</ref><ref name="pmid23580243">{{cite journal |vauthors=Ohman L, Simrén M |title=Intestinal microbiota and its role in irritable bowel syndrome (IBS) |journal=Curr Gastroenterol Rep |volume=15 |issue=5 |pages=323 |year=2013 |pmid=23580243 |doi=10.1007/s11894-013-0323-7 |url=}}</ref><ref name="pmid17148502">{{cite journal |vauthors=Posserud I, Stotzer PO, Björnsson ES, Abrahamsson H, Simrén M |title=Small intestinal bacterial overgrowth in patients with irritable bowel syndrome |journal=Gut |volume=56 |issue=6 |pages=802–8 |year=2007 |pmid=17148502 |pmc=1954873 |doi=10.1136/gut.2006.108712 |url=}}</ref><ref name="pmid22180058">{{cite journal |vauthors=Jeffery IB, O'Toole PW, Öhman L, Claesson MJ, Deane J, Quigley EM, Simrén M |title=An irritable bowel syndrome subtype defined by species-specific alterations in faecal microbiota |journal=Gut |volume=61 |issue=7 |pages=997–1006 |year=2012 |pmid=22180058 |doi=10.1136/gutjnl-2011-301501 |url=}}</ref><ref name="pmid19457422">{{cite journal |vauthors=Spiller R, Garsed K |title=Postinfectious irritable bowel syndrome |journal=Gastroenterology |volume=136 |issue=6 |pages=1979–88 |year=2009 |pmid=19457422 |doi=10.1053/j.gastro.2009.02.074 |url=}}</ref><ref name="pmid25611066">{{cite journal |vauthors=Joo YE |title=Alteration of fecal microbiota in patients with postinfectious irritable bowel syndrome |journal=J Neurogastroenterol Motil |volume=21 |issue=1 |pages=135–7 |year=2015 |pmid=25611066 |pmc=4288086 |doi=10.5056/jnm14133 |url=}}</ref><ref name="pmid10026328">{{cite journal |vauthors=Gwee KA, Leong YL, Graham C, McKendrick MW, Collins SM, Walters SJ, Underwood JE, Read NW |title=The role of psychological and biological factors in postinfective gut dysfunction |journal=Gut |volume=44 |issue=3 |pages=400–6 |year=1999 |pmid=10026328 |pmc=1727402 |doi= |url=}}</ref><ref name="pmid24646319">{{cite journal |vauthors=Nielsen HL, Engberg J, Ejlertsen T, Nielsen H |title=Psychometric scores and persistence of irritable bowel after Campylobacter concisus infection |journal=Scand. J. Gastroenterol. |volume=49 |issue=5 |pages=545–51 |year=2014 |pmid=24646319 |doi=10.3109/00365521.2014.886718 |url=}}</ref> | **[[Immunity (medical)|Immune]] activation due to GI [[infection]] also increases [[Enteroendocrine cells|enteroendocrine]] cells, calprotectin-positive [[Macrophage|macrophages]], [[Intraepithelial lymphocyte|intraepithelial]] [[Lymphocyte|lymphocytes]], and l[[Lamina propria|amina propria]] [[T cell|T cells]] which contribute directly to [[abdominal pain]] perception. <ref name="pmid20101257">{{cite journal |vauthors=Ohman L, Simrén M |title=Pathogenesis of IBS: role of inflammation, immunity and neuroimmune interactions |journal=Nat Rev Gastroenterol Hepatol |volume=7 |issue=3 |pages=163–73 |year=2010 |pmid=20101257 |doi=10.1038/nrgastro.2010.4 |url=}}</ref><ref name="pmid22730468">{{cite journal |vauthors=Simrén M, Barbara G, Flint HJ, Spiegel BM, Spiller RC, Vanner S, Verdu EF, Whorwell PJ, Zoetendal EG |title=Intestinal microbiota in functional bowel disorders: a Rome foundation report |journal=Gut |volume=62 |issue=1 |pages=159–76 |year=2013 |pmid=22730468 |pmc=3551212 |doi=10.1136/gutjnl-2012-302167 |url=}}</ref><ref name="pmid23580243">{{cite journal |vauthors=Ohman L, Simrén M |title=Intestinal microbiota and its role in irritable bowel syndrome (IBS) |journal=Curr Gastroenterol Rep |volume=15 |issue=5 |pages=323 |year=2013 |pmid=23580243 |doi=10.1007/s11894-013-0323-7 |url=}}</ref><ref name="pmid17148502">{{cite journal |vauthors=Posserud I, Stotzer PO, Björnsson ES, Abrahamsson H, Simrén M |title=Small intestinal bacterial overgrowth in patients with irritable bowel syndrome |journal=Gut |volume=56 |issue=6 |pages=802–8 |year=2007 |pmid=17148502 |pmc=1954873 |doi=10.1136/gut.2006.108712 |url=}}</ref><ref name="pmid22180058">{{cite journal |vauthors=Jeffery IB, O'Toole PW, Öhman L, Claesson MJ, Deane J, Quigley EM, Simrén M |title=An irritable bowel syndrome subtype defined by species-specific alterations in faecal microbiota |journal=Gut |volume=61 |issue=7 |pages=997–1006 |year=2012 |pmid=22180058 |doi=10.1136/gutjnl-2011-301501 |url=}}</ref><ref name="pmid19457422">{{cite journal |vauthors=Spiller R, Garsed K |title=Postinfectious irritable bowel syndrome |journal=Gastroenterology |volume=136 |issue=6 |pages=1979–88 |year=2009 |pmid=19457422 |doi=10.1053/j.gastro.2009.02.074 |url=}}</ref><ref name="pmid25611066">{{cite journal |vauthors=Joo YE |title=Alteration of fecal microbiota in patients with postinfectious irritable bowel syndrome |journal=J Neurogastroenterol Motil |volume=21 |issue=1 |pages=135–7 |year=2015 |pmid=25611066 |pmc=4288086 |doi=10.5056/jnm14133 |url=}}</ref><ref name="pmid10026328">{{cite journal |vauthors=Gwee KA, Leong YL, Graham C, McKendrick MW, Collins SM, Walters SJ, Underwood JE, Read NW |title=The role of psychological and biological factors in postinfective gut dysfunction |journal=Gut |volume=44 |issue=3 |pages=400–6 |year=1999 |pmid=10026328 |pmc=1727402 |doi= |url=}}</ref><ref name="pmid24646319">{{cite journal |vauthors=Nielsen HL, Engberg J, Ejlertsen T, Nielsen H |title=Psychometric scores and persistence of irritable bowel after Campylobacter concisus infection |journal=Scand. J. Gastroenterol. |volume=49 |issue=5 |pages=545–51 |year=2014 |pmid=24646319 |doi=10.3109/00365521.2014.886718 |url=}}</ref> | ||
==='''Intrinsic gastrointestinal factors'''=== | ==='''Intrinsic gastrointestinal factors'''=== | ||
*'''Motor abnormalities:''' | |||
**IBS is referred to as ‘[[spastic colon]]’ due to changes in [[Colon (anatomy)|colonic]] [[Motor coordination|motor]] function. | |||
**Manometry recordings from the [[Transverse colon|transverse]], [[Descending colon|descending]] and [[sigmoid colon]] have shown that IBS leads to changed patterns of [[Colon (anatomy)|colonic]] and [[Small intestine|small intestinal]] [[Motor coordination|motor]] function, such as increased frequency and irregularity of [[Lumen|luminal]] contractions. | |||
**[[Muscle|Motor]] changes lead to symptoms of [[diarrhea]] and [[constipation]].<ref name="pmid8789897">{{cite journal |vauthors=Schmidt T, Hackelsberger N, Widmer R, Meisel C, Pfeiffer A, Kaess H |title=Ambulatory 24-hour jejunal motility in diarrhea-predominant irritable bowel syndrome |journal=Scand. J. Gastroenterol. |volume=31 |issue=6 |pages=581–9 |year=1996 |pmid=8789897 |doi= |url=}}</ref><ref name="pmid2865504">{{cite journal |vauthors=Kumar D, Wingate DL |title=The irritable bowel syndrome: a paroxysmal motor disorder |journal=Lancet |volume=2 |issue=8462 |pages=973–7 |year=1985 |pmid=2865504 |doi= |url=}}</ref><ref name="pmid11215731">{{cite journal |vauthors=Simrén M, Castedal M, Svedlund J, Abrahamsson H, Björnsson E |title=Abnormal propagation pattern of duodenal pressure waves in the irritable bowel syndrome (IBS) [correction of (IBD)] |journal=Dig. Dis. Sci. |volume=45 |issue=11 |pages=2151–61 |year=2000 |pmid=11215731 |doi= |url=}}</ref> | |||
**[[Diarrhea]]-prone IBS patients have increased responses to [[ingestion]], [[Corticotropin-releasing hormone|CRH]] ([[Corticotropin-releasing hormone|corticotropin releasing hormone]]), [[Cholecystokinin|CCK]] ([[cholecystokinin]]), which increase the peak amplitude of high-amplitude propagating [[Contraction|contractions]] (HAPCs) and lead to [[Abdominal pain|abdominal discomfort]] with accelerated transit through the [[Colon (anatomy)|colon]]. <ref name="pmid11374689">{{cite journal |vauthors=Chey WY, Jin HO, Lee MH, Sun SW, Lee KY |title=Colonic motility abnormality in patients with irritable bowel syndrome exhibiting abdominal pain and diarrhea |journal=Am. J. Gastroenterol. |volume=96 |issue=5 |pages=1499–506 |year=2001 |pmid=11374689 |doi=10.1111/j.1572-0241.2001.03804.x |url=}}</ref><ref name="pmid7379673">{{cite journal |vauthors=Whitehead WE, Engel BT, Schuster MM |title=Irritable bowel syndrome: physiological and psychological differences between diarrhea-predominant and constipation-predominant patients |journal=Dig. Dis. Sci. |volume=25 |issue=6 |pages=404–13 |year=1980 |pmid=7379673 |doi= |url=}}</ref><ref name="pmid9691924">{{cite journal |vauthors=Fukudo S, Nomura T, Hongo M |title=Impact of corticotropin-releasing hormone on gastrointestinal motility and adrenocorticotropic hormone in normal controls and patients with irritable bowel syndrome |journal=Gut |volume=42 |issue=6 |pages=845–9 |year=1998 |pmid=9691924 |pmc=1727153 |doi= |url=}}</ref><ref name="pmid18456567">{{cite journal |vauthors=Camilleri M, McKinzie S, Busciglio I, Low PA, Sweetser S, Burton D, Baxter K, Ryks M, Zinsmeister AR |title=Prospective study of motor, sensory, psychologic, and autonomic functions in patients with irritable bowel syndrome |journal=Clin. Gastroenterol. Hepatol. |volume=6 |issue=7 |pages=772–81 |year=2008 |pmid=18456567 |pmc=2495078 |doi=10.1016/j.cgh.2008.02.060 |url=}}</ref><ref name="pmid3569764">{{cite journal |vauthors=Kellow JE, Phillips SF |title=Altered small bowel motility in irritable bowel syndrome is correlated with symptoms |journal=Gastroenterology |volume=92 |issue=6 |pages=1885–93 |year=1987 |pmid=3569764 |doi= |url=}}</ref> | |||
**[[Constipation]]-prone [[Irritable bowel syndrome|IBS]] patients show fewer high-amplitude propagating [[Contraction|contractions]] (HAPCs) as compared to [[diarrhea]] prone [[Irritable bowel syndrome|IBS]] patients, delayed transit through the [[Colon (anatomy)|colon]] and decreased [[motility]]. | |||
***Changes in the [[Muscle|motor]] function of the [[Colon (anatomy)|colon]] are responsible for producing the [[Gastrointestinal tract|gastrointestinal]] symptoms of [[Irritable bowel syndrome|IBS]] such as altered [[Intestine|bowel]] habits and [[abdominal pain]].<ref name="pmid18456567" /> | ***Changes in the [[Muscle|motor]] function of the [[Colon (anatomy)|colon]] are responsible for producing the [[Gastrointestinal tract|gastrointestinal]] symptoms of [[Irritable bowel syndrome|IBS]] such as altered [[Intestine|bowel]] habits and [[abdominal pain]].<ref name="pmid18456567" /> | ||
**'''Visceral hypersensitivity:''' | **'''Visceral hypersensitivity:''' | ||
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{{familytree/end}} | {{familytree/end}} | ||
<br><br><br> | <br><br><br> | ||
*'''[[Immune]] activation and [[mucosal]] [[inflammation]]'''{{Family tree/start}} | |||
{{Family tree | A01 |-|-| A02 |-|-|-| A03 | |A01= '''[[Mast cells]]'''| A02= '''[[IMMUNE]] ACTIVATION AND [[MUCOSAL]] [[INFLAMMATION]]'''| A03='''[[Lymphocytes]]'''}} | {{Family tree | A01 |-|-| A02 |-|-|-| A03 | |A01= '''[[Mast cells]]'''| A02= '''[[IMMUNE]] ACTIVATION AND [[MUCOSAL]] [[INFLAMMATION]]'''| A03='''[[Lymphocytes]]'''}} | ||
Revision as of 02:17, 31 October 2017
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:
Overview
IBS is caused by the complex interaction of various factors such as intrinsic gastrointestinal factors, CNS dysregulation and psychosocial factors, genetic and environmental factors. Intrinsic gastrointestinal factors include motor abnormalities, visceral hypersensitivity, immune activation and mucosal inflammation, altered gut microbiota and abnormal serotonin pathways. Visceral hypersensitivity is a decreased threshold for the perception of visceral stimuli that affects spinal excitability brain stem and cortical modulation, activation of specific gastrointestinal mediators and recruitment of peripheral silent nociceptors. Immune activation and mucosal inflammation involves an interaction of lymphocytes, mast cells and proinflammatory cytokines. Environmental factors encompass dietary changes and infections. Psychosocial factors such as stress, anxiety and depression directly shape adult connectivity in the executive control network consisting of structures such as the insula, anterior cingulate cortex and the thalamus. Semipermanent/permanent changes in complex neural circuits lead to central pain amplification and contribute to abdominal pain in IBS patients. The dorsolateral prefrontal cortex activity (responsible for vigilance and alertness of the human brain) and the mid-cingulate cortex (engaged in attention pathways and responses) is reduced in IBS patients, which may lead to alterations in the subjective sensations of pain. Genetic factors also play a role in IBS. It has high twin concordance and familial aggregation. It is associated with Single nucleotide polymorphisms (SNPs) in genes involved in immune activation, neuropeptide hormone function, oxidative stress, nociception, permeability of the GI tract, host-microbiota interaction, inflammation, and TNF activity.
Pathophysiology
Pathogenesis
IBS is an interplay between four main factors:
| CNS dysregulation and psychosocial factors | |||||||||||||||||||||||||||||
| Intrinsic gastrointestinal factors: • Motor abnormalities • Visceral hypersensitivity • Immune activation and mucosal inflammation • Altered gut microbiota • Abnormal serotonin pathways | IRRITABLE BOWEL SYNDROME | Genetic factors: • Twin concordance • Familial aggregation • Single Nucleotide Polymorphisms(SNPs) • TNF polymorphism | |||||||||||||||||||||||||||
| Environmental factors | |||||||||||||||||||||||||||||
Environmental factors
- Diet
- Fermentable oligosaccharides, monosaccharides, disaccharides, and polyols (FODMAPs) are present in stone fruits, artificial sweeteners, lactose-containing foods, and legumes. Changes in diet such as increased amounts (FODMAPs) can alter gut microflora.[1]
- Fermentation and osmotic effects of FODMAPs produce abdominal discomfort and diarrhea in IBS.
- FODMAPs yield carbon dioxide, methane, and hydrogen that are responsible for bloating.
- Osmotically active carbohydrate by products lead to diarrhea by enhancing intestinal contractions and precipitating fluid secretion.[2][3][4][5][6][7][8][9]
- Infection
- Infectious gastroenteritis triggers micro inflammation, and up to one third of irritable bowel syndrome cases follow acute gastroenteritis.
- Micro inflammation of the gut causes activation of the lymphocytes, mast cells and pro inflammatory cytokines that stimulate the enteric nervous system and lead to abnormal visceral and motor responses within the gastrointestinal tract.
- Immune activation due to GI infection also increases enteroendocrine cells, calprotectin-positive macrophages, intraepithelial lymphocytes, and lamina propria T cells which contribute directly to abdominal pain perception. [10][11][12][13][14][15][16][17][18]
Intrinsic gastrointestinal factors
- Motor abnormalities:
- IBS is referred to as ‘spastic colon’ due to changes in colonic motor function.
- Manometry recordings from the transverse, descending and sigmoid colon have shown that IBS leads to changed patterns of colonic and small intestinal motor function, such as increased frequency and irregularity of luminal contractions.
- Motor changes lead to symptoms of diarrhea and constipation.[19][20][21]
- Diarrhea-prone IBS patients have increased responses to ingestion, CRH (corticotropin releasing hormone), CCK (cholecystokinin), which increase the peak amplitude of high-amplitude propagating contractions (HAPCs) and lead to abdominal discomfort with accelerated transit through the colon. [22][23][24][25][26]
- Constipation-prone IBS patients show fewer high-amplitude propagating contractions (HAPCs) as compared to diarrhea prone IBS patients, delayed transit through the colon and decreased motility.
- Changes in the motor function of the colon are responsible for producing the gastrointestinal symptoms of IBS such as altered bowel habits and abdominal pain.[25]
- Visceral hypersensitivity:
- IBS is associated with a decreased threshold for perception of visceral stimuli (i.e. visceral hypersensitivity)[25][27][28]
- Rectal distension produces painful and non-painful sensations at lower volumes in IBS patients as compared to healthy controls, suggesting the presence of afferent pathway disturbances in visceral innervation[29][30][31][32].
- Visceral hypersensitivity contributes to IBS by involving the following:
- Spinal hyperexcitability
- Secondary to activation of neurotransmitters such as:
- N-methyl D aspartate (NMDA) receptor
- nitric oxide
- Activation of specific gastrointestinal mediators that lead to afferent nerve fiber sensitization:
- Central (brainstem and cortical) modulation with increased activation of anterior cingulate cortex, thalamus and insula.
- These structures are involved in processing of pain.
- Cortical and brain stem modulation translate into long term hypersensitivity due to neuroplasticity.
- Semi permanent changes(seen on functional magnetic resonance imaging and positron emission tomography) in the neural response to visceral stimulation contribute to visceral hypersensitivity.[27][33]
- Recruitment of peripheral silent nociceptors cause increased end organ sensitivity due to
- hormonal activation ( increased serotonin affects gastrointestinal motility and visceral pain perception)
- immune activation(recruitment of inflammatory mediators)[27]
- Spinal hyperexcitability
| Spinal hyperexcitability | Activation of • N-methyl D aspartate (NMDA) receptor • nitric oxide | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Central (brainstem and cortical) modulation | Increased activation of: • Anterior cingulate cortex • Thalamus • insula | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Visceral hypersensitivity | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Activation of specific gastrointestinal mediators | Kinins and serotonin activation lead to afferent nerve fiber sensitization | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Recruitment of peripheral silent nociceptors | Increased end organ sensitivity due to hormonal or immune activation | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
- Immune activation and mucosal inflammation
Mast cells IMMUNE ACTIVATION AND MUCOSAL INFLAMMATION Lymphocytes Proinflammatory cytokines - IBS in patients with history of inflammatory bowel disease, celiac disease or microscopic colitis points towards the fact that immune activation and local GI mucosal inflammation play an important role in its pathogenesis.[34][35][36][37][38][39][36]
- IBS patients have higher mucosal counts of lymphocytes (T cells, B cells), mast cells and immune mediators such as prostanoids, proteases, cytokines and histamines.[36][40][41][42][43]
- Lymphocytes:
- Activation of humoral immunity in IBS is specific for the gastrointestinal tract. Increased number of lymphocytes have been found in the small intestine and colon of IBS patients.[35][37][44][45]
- IBS patients with diarrhea have enhanced mucosal humoral activity, associated with activation and proliferation of B cells and immunoglobulin production, identified by microarray profiling.[45]
- IBS patients with severe disease have an increase in lymphocyte infiltration in the myentric plexus.[37]
- Mediators released by lymphocytes include histamine, proteases and nitric oxide. The stimulation of the enteric nervous system by these mediators leads to abnormal visceral and motor responses within the gastrointestinal tract.[35]
- Stool in patients with diarrhea prominent IBS demonstrates high levels of serine protease activity, which is produced by lymphocytes.[46][47]
- In response to high levels of serine protease, there is increased visceral pain and colonic cellular permeability. [46]
- Serine protease inhibitors prevent effects mediated by high levels of serine protease in IBS patients.[47][46]
- Mast cells:
- IBS leads to an increased number of mast cells in IBS patients in the jejunum, terminal ileum and colon.[39]
- Higher numbers of activated mast cells are found in proximity to colonic nerve fibres in the mucosa of the gastrointestinal tract of IBS patients. [39][38]
- Proinflammatory cytokines:
- Cytokines are protein mediators of the immune response. Increased levels of cytokines have been found in IBS patients.[43][42]
- Higher amounts of tumor necrosis factor are produced by the peripheral blood mononuclear cells of IBS patients.[48][36]
- Other cytokines such as interleukin 1β, interleukin 6, interleukin10, and TNFα are raised in IBS patients.
- Increased concentration of cytokines is directly proportional to the severity and frequency of pain.[36][49][48]
- The TNF antagonist infliximab counteracts pain in IBS patients, proving TNF involvement in mechanical hypersensitivity of the colonic afferent nerve endings . [49]
- Altered gut microbiota
- Fecal microflora in IBS patients differ from healthy individuals. Some IBS patients have colonic spirochaetosis, with a unique pathology of increased lymphoid follicles and eosinophils on histology.[40][50] [51][52][53][54][14][55]
- Acute GI infection alters gut microflora switches on a T-helper-2 immune-cell response with increased numbers of CD8 and CD4RA-positive intraepithelial lymphocytes, causing increased susceptibility to the development of IBS. [56][57][58]
- Altered gut microbiota causes increased colonic hypersensitivity. [59]
- Abnormal serotonin pathways
- Serotonin(5-HT) is an important neurotransmitter produced by the enterochromaffin cells in the colon, in response to chemical stimuli (short chain fatty acids produced by gastrointestinal microflora ) and mechanical stimuli ( food) and is increased in IBS patients.[60][61][62][63][64][65][66]
- Serotonin affects gastrointestinal motility and visceral pain perception. Spontaneous release of 5-HT correlates with abdominal pain severity.[67]
- There is an established relationship between IBS and polymorphisms in the gene for serotonin transport causing alteration in intestinal peristalsis due to change in the serotonin reuptake efficacy.[68][69][70][71]
- Increased serotonin production contributes to postprandial symptoms in IBS patients, hence providing the rationale for the therapeutic efficacy of 5-HT 3 receptor antagonists and 5-HT 4 receptor agonists on symptoms in IBS patients.[72][73]
Psychosocial factors and CNS dysregulation
- Symptom exacerbation occurs in IBS patients with emotional disturbances,stress, anxiety or depression. Traumatic experiences before 18 years of age directly shape adult connectivity in the executive control network consisting of structures such as the insula, anterior cingulate cortex and the thalamus.
- Semipermanent/permanent changes in complex neural circuits lead to central pain amplification and contribute to abdominal pain in IBS patients.[74][75]
- The dorsolateral prefrontal cortex activity (responsible for vigilance and alertness of the human brain) and the mid-cingulate cortex (engaged in attention pathways and responses) is reduced in IBS patients, seen on advanced brain imaging techniques as irregularities in the mid- cingulate cortex and prefrontal cortex on diffusion tensor imaging. [76]
- prefrontal cortex modulation may lead to increased perception of visceral pain.
- Modulation of the mid-cingulate cortex is associated with alterations in the subjective sensations of pain.[77][78]
- Patients with IBS have aberrant processing of central information, with decreased feedback on the emotional arousal network that controls the autonomic activity of the gastrointestinal tract and changes gut motility.[79][80]
- IBS is a brain gut disorder as rectal distension in patients causes increased engagement of regions of the brain associated with attentional and behavioral responses.[77][81][82]
- Psychological stress also impacts the release of gut proinflammatory cytokines, contributing to pain in IBS patients.[34]
Genetic factors
- IBS has high twin concordance and familial aggregation:[83][84][85][86][87][88]
- IBS has higher concordance in monozygotic as compared to dizygotic twins.[83][84][85][89]
- Individuals with a biologic relative with IBS have two times a higher risk of developing IBS. [90]
- Single nucleotide polymorphisms (SNPs) in genes:
- IBS has SNPs in genes playing an important role in host-microbiota interaction (TLR9, IL-6 and CDH1), immune activation and epithelial barriers.
- SNPs cause inflammation and increased permeability of the GI tract, leading to abdominal discomfort and increased motility.[91][92]
- Mutation of type V (alpha subunit) of SCN5A-encoded voltage gated sodium channel causes IBS.[93][94]
- Genome wide DNA methylation profiling is impaired in IBS and this involves genes linked to neuropeptide hormone function and oxidative stress.[95]
- IBS causes mutation in the neuropeptide S receptor gene (NPSR1) involved in nociception, inflammation and anxiety with abdominal pain.[96]
- Genes involved in the regulation of hepatic bile acid synthesis such as a functional Klothoβ gene are mutated in IBS.[97][98]
- TNF polymorphisms:
- SNPs in tumour necrosis factor alpha (TNFα) and genes coding for superfamily member 15 (TNFSF15) have proven associations with IBS.[92][99][100]
- TNF polymorphisms are also associated with post infectious IBS such as rs4263839 in TNFSF15 and IBS, particularly IBS associated with constipation.[100][99]
Gross Pathology
Microscopic Pathology
Microscopic changes that may be found in IBS patients are as follows:[101][17][60][102][103][104][105][106][107][37][108][39]
LOCATION LAYER OF INTESTINE INVOLVED MAST CELLS T LYMPHOCYTES ENTEROCHROMAFFIN CELLS Rectum Mucosa +++/- +/- +/- Terminal ileum Mucosa - ++ - Cecum Mucosa ++ - - Colon Muscularis externa +/- - - Jejunum Myentric plexus ++ - - References
- ↑ Muir JG, Gibson PR (2013). "The Low FODMAP Diet for Treatment of Irritable Bowel Syndrome and Other Gastrointestinal Disorders". Gastroenterol Hepatol (N Y). 9 (7): 450–2. PMC 3736783. PMID 23935555.
- ↑ Böhn L, Störsrud S, Törnblom H, Bengtsson U, Simrén M (2013). "Self-reported food-related gastrointestinal symptoms in IBS are common and associated with more severe symptoms and reduced quality of life". Am. J. Gastroenterol. 108 (5): 634–41. doi:10.1038/ajg.2013.105. PMID 23644955.
- ↑ Young E, Stoneham MD, Petruckevitch A, Barton J, Rona R (1994). "A population study of food intolerance". Lancet. 343 (8906): 1127–30. PMID 7910231.
- ↑ David LA, Maurice CF, Carmody RN, Gootenberg DB, Button JE, Wolfe BE, Ling AV, Devlin AS, Varma Y, Fischbach MA, Biddinger SB, Dutton RJ, Turnbaugh PJ (2014). "Diet rapidly and reproducibly alters the human gut microbiome". Nature. 505 (7484): 559–63. doi:10.1038/nature12820. PMC 3957428. PMID 24336217.
- ↑ Francis CY, Whorwell PJ (1994). "Bran and irritable bowel syndrome: time for reappraisal". Lancet. 344 (8914): 39–40. PMID 7912305.
- ↑ Elli L, Tomba C, Branchi F, Roncoroni L, Lombardo V, Bardella MT, Ferretti F, Conte D, Valiante F, Fini L, Forti E, Cannizzaro R, Maiero S, Londoni C, Lauri A, Fornaciari G, Lenoci N, Spagnuolo R, Basilisco G, Somalvico F, Borgatta B, Leandro G, Segato S, Barisani D, Morreale G, Buscarini E (2016). "Evidence for the Presence of Non-Celiac Gluten Sensitivity in Patients with Functional Gastrointestinal Symptoms: Results from a Multicenter Randomized Double-Blind Placebo-Controlled Gluten Challenge". Nutrients. 8 (2): 84. doi:10.3390/nu8020084. PMC 4772047. PMID 26867199.
- ↑ Coletta M, Gates FK, Marciani L, Shiwani H, Major G, Hoad CL, Chaddock G, Gowland PA, Spiller RC (2016). "Effect of bread gluten content on gastrointestinal function: a crossover MRI study on healthy humans". Br. J. Nutr. 115 (1): 55–61. doi:10.1017/S0007114515004183. PMID 26522233.
- ↑ Yang J, Fox M, Cong Y, Chu H, Zheng X, Long Y, Fried M, Dai N (2014). "Lactose intolerance in irritable bowel syndrome patients with diarrhoea: the roles of anxiety, activation of the innate mucosal immune system and visceral sensitivity". Aliment. Pharmacol. Ther. 39 (3): 302–11. doi:10.1111/apt.12582. PMID 24308871.
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