Irritable Bowel Syndrome: An Overview

Irritable bowel syndrome (IBS) is characterized as one of the disorders of gut-brain interaction, previously known as a functional gastrointestinal (GI) disorder, with the new term acknowledging the relationship between gastrointestinal function and involvement with central nervous system function and psychosocial stressors. Symptoms can range from mild to severe, and may be disabling to a degree that negatively impacts quality of life, self-image, social interactions, and ability to work or travel.¹

In IBS, sensory perception is often abnormal, making the nerves in the bowels more sensitive to stretching or other movement, which may worsen pain and other symptoms. Functioning of the bowels is also abnormal, leading to motility issues such as bowels moving too much or too often, or the opposite issue of not moving enough or often enough.²

Along with recurring symptoms related to the condition, those with IBS are more likely to develop other disorders affecting everyday function, including fibromyalgia and chronic fatigue syndrome.¹

In the past, IBS went by several different names including mucous colitis, spastic colon, nervous colon, spastic bowel, and IBS colitis.³

One important distinction is that the condition is not part of inflammatory bowel disease (IBD) – which comprises Crohn’s disease and ulcerative colitis – although it is sometimes mistakenly grouped together with those conditions. Although there is some overlap in terms of symptoms, and both are considered incurable but manageable, this distinction is important since they require very different treatments.¹

Additionally, IBS is less likely to lead to hospitalization or require surgery compared to IBD, since it does not cause the type of destructive inflammation seen with IBD.¹

Irritable Bowel Syndrome Prevalence

IBS affects between 5% and 10% of individuals worldwide, and can affect adults of both sexes as well as children.^2,4

The NIH reports that these patient populations are more likely to develop IBS:³

• people younger than age 50

• have a family member with IBS

• have a history of stressful or difficult life events, such as abuse, in childhood

• people who have or recently had a severe infection in the digestive tract

Although IBS can affect both sexes, women are up to two times more likely than men to develop the syndrome.³

Irritable Bowel Syndrome Causes and Risk Factors

The cause of IBS remains unknown, but it is believed that symptoms occur due to abnormal functioning or communication between the nervous system and bowel muscles.⁵

This abnormal regulation may result in increased sensitivity in the bowel, leading to loss of coordination in the muscles in the bowel wall. While there is no physical obstruction or signs of tissue damage, a patient may feel sensations that are similar to a blockage, such as intense abdominal cramping and pain.⁵

According to the American Society of Colon & Rectal Surgeons, risk factors include:⁵

• bacterial activity in the gut

• bacterial overgrowth

• food intolerance or sensitivities

• altered ability of the bowel to move freely

• oversensitive intestines

• altered nervous system processing

• altered hormonal regulation

Stress may also play a role in symptom development. While IBS is not caused by stress or anxiety, emotional stress may be a factor for the onset of IBS episodes.⁵

Irritable Bowel Syndrome Symptoms

According to the International Foundation for Gastrointestinal Disorders, the most dominant symptom of IBS is abdominal discomfort or pain that is associated with bowel movements, and this intermittent pain may be accompanied by:^1,2

• diarrhea

• constipation

• alternating episodes of diarrhea and constipation

• bloating or distention of the abdomen

• mucus in the stool

• gassiness

• nausea

• urge to move bowels but unable to have bowel movement

Along with these symptoms, there may also be a sensation of blockage or squeezing of the colon, which can result in cramping. Symptoms can vary from person to person and may change over time, since IBS is a long-term condition.⁵

Subtypes and Comorbidities of IBS

There are three subtypes of IBS, which are based on bowel symptoms:³

• IBS with diarrhea, called IBS-D: symptoms of diarrhea occur most often; more than a quarter of stools are loose or watery and less than a quarter of stools are hard or lumpy

• IBS with constipation, called IBS-C: symptoms of constipation occur most often; more than a quarter of stools are hard or lumpy and less than a quarter of stools are loose or watery

• IBS mixed, called IBS-M: symptoms of both constipation and diarrhea; more than a quarter of stools are hard or lumpy, and more than a quarter of stools are loose or watery

Identifying the subgroup of IBS is helpful since it can drive treatment decisions.² Also worth noting is that many people with IBS have normal bowel movements on some days and abnormal bowel movements on other days, so there does not need to be consecutive days of constipation or diarrhea to be diagnosed with IBS and its subtypes.³

Other conditions that may be present in people with IBS include:³

• fibromyalgia

• chronic pelvic pain

• dyspepsia

• gastroesophageal reflux disease

• chronic fatigue syndrome

People with IBS are also at significant risk for certain mental health disorders such as anxiety, depression, and somatic symptom disorder.³ Overall, people with IBS have a threefold higher risk of anxiety and depression than people without the syndrome. In one meta-analysis, the prevalence of symptoms of anxiety for those with IBS was 39% and depression was 29%. The prevalence of co-occurring anxiety and depressive symptoms was 23%.⁶

Irritable Bowel Syndrome Screening and Diagnosis

Although IBS shares symptoms such as abdominal pain, bloating, and diarrhea with IBD, it is helpful to distinguish IBS from those conditions as part of a diagnostic process. Most notably, IBD has additional symptoms of fever, sudden weight loss, and blood in the stool, which are not considered IBS signs. Also, IBD is an inflammatory autoimmune disease that is characterized by chronic inflammation and visible in the gastrointestinal tract, while the GI tract in IBS will appear normal in screenings.^.2

Criteria for diagnosing IBS include having abdominal discomfort or pain for at least 12 weeks, even if non-consecutive, over the past 12 months. This must be accompanied by at least two of these three symptoms:¹

• relief upon defecation

• onset associated with a change in stool frequency

• onset associated with a change in the form of the stool

Assessing symptoms and determining risk factors are the only way to determine if IBS is present since there is no specific test for the syndrome and a colonoscopy will not present evidence of disease. Imaging tests are often done not to find evidence of IBS, but instead, to rule out other diseases that affect the GI tract.⁴

First-Line Treatments for Irritable Bowel Syndrome

Similar to IBD, there is no cure for IBS but the condition can often be managed in a way that reduces symptom flare-ups. Many people diagnosed with IBS can control their symptoms to some degree through lifestyle changes that include stress management, probiotics in either food or supplements, and identification and avoidance of trigger foods.⁴

There are some medications that may alleviate symptoms, which are tailored to a patient’s specific subtype. These include:⁷

• laxatives

• antidiarrheals

• secretagogues/prosecretory agents

• retainagogues

• antispasmodics, including anticholinergics

• antibiotics

• agonists/antagonists such as 5-hydroxytryptamine (serotonin) 3 receptor antagonists and agonists

Given the higher prevalence of mental health issues in those with IBS, providing mental health resources as part of treatment – such as antidepressants, therapy, or a combination of both – is also a key part of patient support, including prevention of symptom flares.⁶