Functional gastrointestinal disorders (FGID), also known as disorders of gut-brain interaction, include a number of separate idiopathic disorders which affect different parts of the gastrointestinal tract and involve visceral hypersensitivity and motility disturbances.
Functional bowel disorder refer in medicine to a group of bowel 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.
The Rome process, has helped to define the functional gastrointestinal disorders.
The current Rome IV classification:
A. Esophageal disorders
A1. Functional chest pain
A2. Functional heartburn
A3. Reflux hypersensitivity
A5. Functional dysphagia
B. Gastroduodenal disorders
B1. Functional dyspepsia
B1a. Postprandial distress syndrome (PDS)
B1b. Epigastric pain syndrome (EPS)
B2. Belching disorders
B2a. Excessive supragastric belching
B2b. Excessive gastric belching
B3. Nausea and vomiting disorders
B3a. Chronic nausea vomiting syndrome (CNVS)
B3b. Cyclic vomiting syndrome (CVS)
B3c. Cannabinoid hyperemesis syndrome (CHS)
B4. Rumination syndrome
C. Bowel disorders
C1. Irritable bowel syndrome (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
C3. Functional diarrhea
C4. Functional abdominal bloating/distension
C5. Unspecified functional bowel disorder
C6. Opioid-induced constipation
D. Centrally mediated disorders of gastrointestinal pain
D1. Centrally mediated abdominal pain syndrome (CAPS)
D2. Narcotic bowel syndrome (NBS)/ Opioid-induced GI hyperalgesia
E. Gallbladder and sphincter of Oddi disorders
E1. Biliary pain
E1a. Functional gallbladder disorder
E1b. Functional biliary sphincter of Oddi disorder
E2. Functional pancreatic sphincter of Oddi disorder
F. Anorectal disorders
F1. Fecal incontinence
F2. Functional anorectal pain
F2a. Levator ani syndrome
F2b. Unspecified functional anorectal pain
F2c. Proctalgia fugax
F3. Functional defecation disorders
F3a. Inadequate defecatory propulsion
F3b. Dyssynergic defecation
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
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
Functional gastrointestinal disorders are very common. Globally, irritable bowel syndrome and functional dyspepsia alone may affect 16-26% of the population.
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 (CNS-ENS) regulation.
There are complex interactions between these factors through the brain-gut axis.
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.
In FGIDs diet, microbiome, genetics, neuromuscular function and immunological response all interact.