Functional gastrointestinal disorders (FGID), also known as disorders of gut–brain interaction, include a number of separate

idiopathic An idiopathic disease is any disease with an unknown cause or mechanism of apparent spontaneous origin. From Greek ἴδιος ''idios'' "one's own" and πάθος ''pathos'' "suffering", ''idiopathy'' means approximately "a disease of its own kin ...

disorders which affect different parts of the gastrointestinal tract and involve visceral hypersensitivity and

motility Motility is the ability of an organism to move independently, using metabolic energy. Definitions Motility, the ability of an organism to move independently, using metabolic energy, can be contrasted with sessility, the state of organisms th ...

disturbances.

Definition of functional gastrointestinal disorders/disorders of gut-brain interaction

Using the Delphi method, the Rome Foundation and its board of directors, chairs and co-chairs of the ROME IV committees developed the current definition for disorders of gut-brain interaction.Drossman DA. The Rome IV Committees, editor. Functional Gastrointestinal Disorders and the Rome IV process. In: Drossman DA, Chang L, Chey WD, Kellow J, Tack J, Whitehead WE, editors. Rome IV functional gastrointestinal disorders: disorders of gut-brain interaction. I. Raleigh, NC: The Rome Foundation; 2016. pp. 1–32. A group of disorders classified by GI symptoms related to any combination of: * Motility disturbance * Visceral hypersensitivity * Altered mucosal and immune function * Altered gut microbiota * Altered

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all p ...

(CNS) processing

Classification

Terms such as ''functional colonic disease'' (or ''functional bowel disorder'') refer in medicine to a group of

bowel The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans and ...

disorders which are characterised by chronic abdominal complaints without a structural or biochemical cause that could explain symptoms. Other ''functional'' disorders relate to other aspects of the process of

digestion Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intest ...

. The consensus review process of meetings and publications organised by the Rome Foundation, known as the

Rome process The Rome process and Rome criteria are an international effort to create scientific data to help in the diagnosis and treatment of functional gastrointestinal disorders, such as irritable bowel syndrome, functional dyspepsia and rumination syndrom ...

, has helped to define the functional gastrointestinal disorders. Successively, the Rome I, Rome II, Rome III and Rome IV proposed consensual classification system and terminology, as recommended by the Rome Coordinating Committee. These now include classifications appropriate for adults, children and neonates/toddlers. The current ROME IV classification, published in 2016, is as follows: A. Esophageal disorders * A1. Functional chest pain * A2. Functional heartburn * A3.

Reflux Reflux is a technique involving the condensation of vapors and the return of this condensate to the system from which it originated. It is used in industrial and laboratory distillations. It is also used in chemistry to supply energy to reactions ...

hypersensitivity * A4.

Globus Globus is Latin for ''sphere'' or ''globe''. It may also refer to: Business * Globus Medical, a medical device company in Audubon, PA * Globus (clothing retailer), an Indian clothing retail store * Globus (company), a Swiss department store c ...

* A5. Functional

dysphagia Dysphagia is difficulty in swallowing. Although classified under "symptoms and signs" in ICD-10, in some contexts it is classified as a condition in its own right. It may be a sensation that suggests difficulty in the passage of solids or liq ...

B. Gastroduodenal disorders * B1. Functional dyspepsia ** B1a. Postprandial distress syndrome (PDS) ** B1b. Epigastric pain syndrome (EPS) * B2.

Belching Burping (also called belching and eructation) is the release of gas from the upper digestive tract (esophagus and stomach) of animals through the mouth. It is usually audible. In humans, burping can be caused by normal eating processes, or as ...

disorders ** B2a. Excessive supragastric belching ** B2b. Excessive gastric belching * B3.

Nausea Nausea is a diffuse sensation of unease and discomfort, sometimes perceived as an urge to vomit. While not painful, it can be a debilitating symptom if prolonged and has been described as placing discomfort on the chest, abdomen, or back of the ...

and

vomiting Vomiting (also known as emesis and throwing up) is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose. Vomiting can be the result of ailments like food poisoning, gastroenteri ...

disorders ** B3a. Chronic nausea vomiting syndrome (CNVS) ** B3b. Cyclic vomiting syndrome (CVS) ** B3c. Cannabinoid hyperemesis syndrome (CHS) * B4.

Rumination syndrome Rumination syndrome, or merycism, is a chronic motility disorder characterized by effortless regurgitation of most meals following consumption, due to the involuntary contraction of the muscles around the abdomen. There is no retching, nausea, h ...

C. Bowel disorders * C1.

Irritable bowel syndrome Irritable bowel syndrome (IBS) is a "disorder of gut-brain interaction" characterized by a group of symptoms that commonly include abdominal pain and or abdominal bloating and changes in the consistency of bowel movements. These symptoms may ...

(IBS) ** IBS with predominant constipation (IBS-C) ** IBS with predominant diarrhea (IBS-D) ** IBS with mixed bowel habits (IBS-M) ** IBS unclassified (IBS-U) * C2. Functional

constipation Constipation is a bowel dysfunction that makes bowel movements infrequent or hard to pass. The stool is often hard and dry. Other symptoms may include abdominal pain, bloating, and feeling as if one has not completely passed the bowel movement ...

* C3. Functional

diarrhea Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin w ...

* C4. Functional abdominal

bloating Abdominal bloating (or simply bloating) is a short-term disease that affects the gastrointestinal tract. Bloating is generally characterized by an excess buildup of gas, air or fluids in the stomach. A person may have feelings of tightness, pres ...

/distension * C5. Unspecified functional bowel disorder * C6. Opioid-induced constipation D. Centrally mediated disorders of gastrointestinal pain * D1. Centrally mediated

abdominal pain Abdominal pain, also known as a stomach ache, is a symptom associated with both non-serious and serious medical issues. Common causes of pain in the abdomen include gastroenteritis and irritable bowel syndrome. About 15% of people have a m ...

syndrome (CAPS) * D2. Narcotic bowel syndrome (NBS)/ Opioid-induced GI hyperalgesia E. Gallbladder and sphincter of Oddi disorders * E1. Biliary pain ** E1a. Functional

gallbladder In vertebrates, the gallbladder, also known as the cholecyst, is a small hollow organ where bile is stored and concentrated before it is released into the small intestine. In humans, the pear-shaped gallbladder lies beneath the liver, although ...

disorder ** E1b. Functional biliary

sphincter of Oddi The sphincter of Oddi (also hepatopancreatic sphincter or Glisson's sphincter), abbreviated as SO, is a muscular valve that in some animals, including humans, controls the flow of digestive juices (bile and pancreatic juice) out of the pancreas ...

disorder * E2. Functional

pancreatic The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an endocr ...

sphincter of Oddi disorder F. Anorectal disorders * F1.

Fecal incontinence Fecal incontinence (FI), or in some forms encopresis, is a lack of control over defecation, leading to involuntary loss of bowel contents, both liquid stool elements and mucus, or solid feces. When this loss includes flatus (gas), it is referre ...

* F2. Functional anorectal pain ** F2a.

Levator ani The levator ani is a broad, thin muscle group, situated on either side of the pelvis. It is formed from three muscle components: the pubococcygeus, the iliococcygeus, and the puborectalis. It is attached to the inner surface of each side of the ...

syndrome ** F2b. Unspecified functional anorectal pain ** F2c.

Proctalgia fugax Proctalgia fugax, a variant of levator ani syndrome, is a severe, episodic pain in the regions of the rectum and anus. It can be caused by cramping of the levator ani muscle, particularly in the pubococcygeal part. Signs and symptoms It most of ...

* F3. Functional defecation disorders ** F3a. Inadequate defecatory propulsion ** F3b.

Dyssynergic defecation Obstructed defecation syndrome (abbreviated as ODS, with many synonymous terms) is a major cause of functional constipation (primary constipation), of which it is considered a subtype. It is characterized by difficult and/or incomplete emptying of ...

G. Childhood functional GI disorders: Neonate/Toddler * G1. Infant regurgitation * G2. Rumination syndrome * G3. Cyclic vomiting syndrome (CVS) * G4. Infant colic * G5. Functional diarrhea * G6. Infant dyschezia * G7. Functional constipation H. Childhood functional GI disorders: Child/Adolescent * H1. Functional nausea and vomiting disorders ** H1a. Cyclic vomiting syndrome (CVS) ** H1b. Functional nausea and functional vomiting *** H1b1. Functional nausea *** H1b2. Functional vomiting ** H1c. Rumination syndrome ** H1d.

Aerophagia Aerophagia (or aerophagy) is a condition of excessive air swallowing, which goes to the stomach instead of the lungs. Aerophagia may also refer to an unusual condition where the primary symptom is excessive flatus (farting), belching (burping) is ...

* H2. Functional abdominal pain disorders ** H2a. Functional dyspepsia *** H2a1. Postprandial distress syndrome *** H2a2. Epigastric pain syndrome ** H2b. Irritable bowel syndrome (IBS) ** H2c. Abdominal migraine ** H2d. Functional abdominal pain ‒ NOS * H3. Functional defecation disorders ** H3a. Functional constipation ** H3b. Nonretentive fecal incontinence

Causes

FGIDs share in common any of several physiological features including increased motor reactivity, enhanced visceral hypersensitivity, altered mucosal immune and inflammatory function (associated with bacterial dysbiosis), and altered central nervous system and

enteric nervous system The enteric nervous system (ENS) or intrinsic nervous system is one of the main divisions of the autonomic nervous system (ANS) and consists of a mesh-like system of neurons that governs the function of the gastrointestinal tract. It is capable of ...

(CNS-ENS) regulation. The pathophysiology of FGID has been best conceptualized using biopsychosocial model help to explain the relationships between an individual factors in their early life that in turn can influence their psychosocial factor and physiological functioning. This model also shows the complex interactions between these factors through the brain-gut axis.Drossman DA. The Rome IV Committees, editor. Functional Gastrointestinal Disorders and the Rome IV process. In: Drossman DA, Chang L, Chey WD, Kellow J, Tack J, Whitehead WE, editors. Rome IV functional gastrointestinal disorders: disorders of gut-brain interaction.I. Raleigh, NC: The Rome Foundation; 2016. pp 1–32. These factors affect how FGID manifest in terms of symptoms but also affect the clinical outcome. These factors are interconnected and the influences on these factors are bidirectional and mutually interactive.

Early life factors

Early life factors include genetic factors, psychophysiological and sociocultural factors, and environmental exposures. * Genetics – Several polymorphisms and candidate genes may predispose individuals to develop FGID. These include alpha-2 adrenergic and

5-HT receptor 5-HT receptors, 5-hydroxytryptamine receptors, or serotonin receptors, are a group of G protein-coupled receptor and ligand-gated ion channels found in the central and peripheral nervous systems. They mediate both excitatory and inhibitory ne ...

s; serotonin and

norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter. The name "noradrenaline" (from Latin '' ad' ...

transporters (SERT, NET); inflammatory markers interleukin-(IL)10, tumor necrosis factor-(TNF) alpha, and TNF super family member 15 (TNF-SF15); intracellular cell signaling (

G protein G proteins, also known as guanine nucleotide-binding proteins, are a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior. Their a ...

s); and ion channels (SCN5A). However, the expression of a FGID requires the influence of additional environmental exposures such as infection, illness modeling and other factors. * Psychophysiological factors may affect the expression of these genes, thus leading to symptoms production associated with FGID. * Sociocultural factors and family interactions have been shown to shape later reporting of symptoms, the development of FGIDs, and health care seeking. The expression of pain varies across cultures as well including denial of symptoms to dramatic expression. * Environmental exposures – Prior studies have shown the effect of environmental exposures in relation to the development of FGIDs. Environmental exposures such as childhood salmonella infection can be a risk factor for IBS in adulthood.

Psychosocial factors

Psychosocial factors influence the functioning of the GI tract through the brain-gut axis (motility, sensitivity, barrier function). They also affect experience and behavior, treatment selection and the clinical outcome. Psychological stress or one's emotional response to stress exacerbates gastrointestinal symptoms and may contribute to FGID development.

Physiology

The physiology of FGID is characterized by abnormal motility, visceral hypersensitivity as well as dysregulation of the immune system and barrier function of the GI tract as well as inflammatory changes. * Abnormal motility
Studies have shown altered muscle contractility and tone, bowel compliance, and transit may contribute to many of the gastrointestinal symptoms of FGID which may include diarrhea, constipation, and vomiting. * Visceral hypersensitivity
In FGID there is poor association of pain with GI motility in many functional GI disorders. These patient often have a lower pain threshold with balloon distension of the bowel (visceral hyperalgesia), or they have increased sensitivity even to normal intestinal function; Visceral hypersensitivity may be amplified in patients with FGIDs. * Immune dysregulation, inflammation, and barrier dysfunction
Studies on postinfectious IBS have shown that factors such as mucosal membrane permeability, the intestinal flora, and altered mucosal immune function. Ultimately leading to visceral hypersensitivity. Factors contributing to this occurrence include genetics, psychological stress, and altered receptor sensitivity at the gut mucosa and myenteric plexus, which are enabled by mucosal immune dysfunction. * Microbiome
There has been increased attention to the role of bacteria and the microbiome in overall health and disease. There is evidence for a group of microorganisms which play a role in the brain-gut axis. Studies have revealed that the bacterial composition of the gastrointestinal tract in IBS patient differs from healthy individuals (e.g., increased Firmicutes and reduced Bacteroidetes and Bifidobacteria) However, further research is needed to determine the role of the microbiome in FGIDs. * Food and diet
The types of food consumed and diet consumed plays a role in the manifestation of FGID and also their relationship to intestinal microbiota. Studies have shown that specific changes in diet (e.g., low FODMAP—fermentable oligo-, di-, and monosaccharides and polyols, or gluten restriction in some patients) may help and reduce the symptom burden in FGID. However, no one diet has been shown to be recommended for all people.

Brain-gut axis

The brain-gut axis is the mechanism in which the psychosocial factors influence the GI tract and vice versa. There is communication between emotional and cognitive centers of the brain to the GI tract and vice versa. Emotions have been shown to stimulate colon motor function and result in decreased colonic transit time, increased contractile activity, the induction of defecation, and symptoms of diarrhea.

Epidemiology

Functional gastrointestinal disorders are very common. Globally, irritable bowel syndrome and functional dyspepsia alone may affect 16–26% of the population.

Research

There is considerable research into the causes, diagnosis and treatments for FGIDs. Diet, microbiome, genetics, neuromuscular function and immunological response all interact. A role for mast cell activation has been proposed as one of the factors.

References

External links

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