Functional GI disorders

This blog series is based on the Gastroenterology Journal, Annual special on the topic of functional gut disorders

 The gastrointestinal (GI) tract is a continuous tube that connects the mouth to the anus. Its walls contain a layer of muscles, which can contract and relax in a coordinated fashion to convey food. These muscles are directly connected to the central nervous system (CNS).

The inner linings of the GI tract are known as mucosa, which come into direct contact with gut contents. Sitting on the mucosa, there are “friendly” microbes (bacteria) that help us digest food and prevent the persistence of harmful microbes.

Functional gastrointestinal disorders (FGIDs) are defined as “a group of disorders characterised by GI symptoms related to any combination of the following:

• Motility disturbance: abnormal, un-coordinated spasms of the gut muscles. This can cause a variety of symptoms including nausea, vomiting, abdominal pain and diarrhoea.
• Visceral hypersensitivity: increased sensitivity to pain by internal organs. Otherwise innocuous stimuli may cause (significant) discomfort. In addition, visceral hypersensitivity means a lower pain threshold. As such, minimally invasive procedures (such as balloon distensions of the bowel) cause more pain, and for longer periods
• Altered mucosal and immune function: reduced ability to “filter out” harmful pathogens, which make people more prone to gastrointestinal infections.
• Altered gut microbiota: It is likely that microbes living within the gut can influence the link between central nervous system and the GI tract. In FGIDs, the bacterial composition of the gut often changes, and this may be responsible, at least in part, for the symptoms experienced by FGID sufferers.
• Altered central nervous system (CNS) processing: changes in the brain affecting the secretory, sensory and motility functions of the gut. For example, anxiety and stress can delay the time it takes for the stomach to empty and induce defecation. The interaction between the gut and the brain goes both ways; changes in gut motility can disrupt cognitive functioning, and cause feelings such as anxiety and depression

FGIDs can affect any segment of the gut including the oesophagus, stomach and bowels. The best-understood example of FGID is irritable bowel syndrome (IBS), however many other examples exist. In  total there are 33 adult, and 20 paediatric categories of FGID.  

Unfortunately, FGIDs are not associated with structural or chemical changes, so imaging and blood tests are rendered useless for diagnosing FGIDs, and they are done to rule out more serious problems such as inflammation or cancer. As such, the diagnosis is typically a clinical one, based on medical history and the symptoms reported by patients, although certain tests can be helpful in showing that a suspected FGID such as irritable bowel syndrome is actually due to something else such as small intestinal bacterial overgrowth, a common condition which is frequently overlooked.

Symptoms of FGID

FGIDs are associated with a wide variety of symptoms including

• Functional indigestion (dyspepsia)
• Abdominal pain
• Functional diarrhoea
• Functional constipation
• Functional vomiting

The term ‘functional’ means that there is no underlying physical or physiological cause.

Some FGIDs patients present with a single symptom (e.g: functional constipation). Others may have two or more symptoms.

The symptoms associated with FGIDs can be classified as mild, moderate and severe. The different severity levels are determined by  the number of symptoms experienced, other than abdominal pain.

Although both men and women, of any age, can suffer from FGIDs, women are more likely to suffer from moderate-severe symptoms than men. Younger people are also more likely to suffer from severe FGID than older people. The reason for this is somewhat unclear but may relate to greater nerve sensitivity in youth.

Treatment of symptoms

Treatment for FGID varies according to the level of severity.

For people with mild symptoms, treatment strategies include:

• Educating individuals about the disease to help them understand the symptoms and why they’re experiencing them
• Reassuring individuals and answering any of  their concerns  
• Modifying diet and lifestyle habits that may worsen symptoms of FGID, including alcohol, fatty foods and dairy products

Moderate symptoms: in addition to the above, the following interventions are suggested:

• Ask the patient to keep a symptom diary (for 1-2 weeks) to observe for particular patterns
• Trial of medications to reduce the impact of symptoms on the quality of life, such as medicines to relieve cramps or to reduce the size of gas bubbles in the gut (peppermint is particularly good at doing this)
• Psychological therapies may be appropriate for patients, especially those experiencing pain. Some of these have been proven in high quality medical trials to be very successful in some groups of patients.

Severe symptoms: in addition to the above, the following interventions are suggested:

• Drugs to reduce visceral sensitivity. Some of these are more typically used as anti-depressants but they can be very effective at doses typically lower than used to treat depression, especially in patients suffering from chronic, moderate-severe pain
• Referral to specialised clinics that provide a multi-disciplinary approach to FGID