What Is Irritable Bowel Syndrome (IBS)?

I. Definition : 

 Irritable syndrome is a functional bowel disorder that most patients who come to the hospital complaining about abdominal pain or discomfort in the absence of detectable abnormality in the body.
Throughout the world, around 10 to 20% of adults and adolescents have symptoms consistent with IBS ( Irritable bowel syndrome) and mostly affects the only female.

IBS can be confused with other functional disorders such as fibromyalgia, headache, backache, and genitourinary symptoms. 

Diagnostic criteria for irritable bowel syndrome
Recurrent abdominal pain or discomfort at least 3 days per month in the last 3 months and can be associated with 2 or more of the following : 1/. Improvement with defecation 2/. Changes in frequency of stool 3/. Change in the form ( appearance ) of stool

II. Clinical findings :

 Irritable bowel syndrome ( IBS ) affects all ages, most of the patients have the symptoms before age 45. Women are diagnosed with IBS 2 times as often as men and makeup 80% of patients with severe IBS.
Pain or abdominal discomfort is a key symptom for the diagnosis of IBS. These symptoms often improve with defecation and are associated with changes in frequency or form of stool.
 Abdominal Pain :

Abdominal pain in IBS is highly variable in intensity and location. It is frequently episodic and crampy but it is also a constant ache.
Patients with severe IBS frequently wake repeatedly during the night.
Pain is often exacerbated by eating or emotional stress and improved by the passage of flatus or stools.
 Altered Bowel Habits :
Constipation alternating with diarrhea is one of the most common patterns in IBS. Stools are usually hard with narrowed caliber. Diarrhea in IBS usually consists of small volumes of loose stools. Diarrhea may be aggravated by emotional stress or eating. Moreover, stools contain large amounts of mucus.
 Gas and flatulence :
Most IBS patients complain about not having gas and abdominal distension, patients with IBS tend to reflux gas from the distal to the more proximal intestine, which may explain the belching.
 Upper Gastrointestinal Symptoms :
50% of the patients with IBS complain of dyspepsia, heartburn, nausea, and vomiting. The prevalence of IBS is higher among patients with dyspepsia than among those who reported no symptoms of dyspepsia.

III. Pathophysiology :

The pathogenesis of IBS can be associated with abnormal gut motor and sensory activity, central neural dysfunction, psychological disturbances, stress, and luminal factors have been proposed.IBS patients may exhibit increased rectosigmoid motor activity for up to 3 h after eating.
According to studies of motor activity, IBS patients frequently exhibit exaggerated sensory responses to visceral stimulation. Postprandial pain has been temporally related to the entry of the food bolus into the cecum in 74% of patients. In addition, IBS patients have an increased area of referred pain after lipid ingestion that was not observed in healthy individuals.
The role of the central nervous system (CNS) factor in the pathogenesis of IBS is strongly suggested by the association of emotional disorders and stress with symptom exacerbation and the therapeutic response to therapies that act on cerebral cortical sites. In IBS patients show preferential activation of the prefrontal lobe, which contains a vigilance network within the brain that increases alertness. This can lead to an increased perception of visceral pain. Psychological factors influence pain thresholds in IBS patients, as stress alters sensory thresholds. The pathophysiologic relationship between IBS and sexual or physical abuse is unknown.
Patients with IBS frequently demonstrate increased motor reactivity of the colon and small bowel to a variety of stimuli and altered visceral sensation associated with lowered sensation thresholds. These may result from CNS-enteric nervous system dysregulation.
IBS can induce gastrointestinal (GI) infection. According to researchers, the patients confirmed bacterial gastroenteritis. The microbes involved in the initial infection are Campylobacter, Salmonella, and Shigella. Campylobacter enteritis could persist for more than a year and may contribute to post-infective IBS. Serotonin (5HT)-containing enterochromaffin cells in the colon is increased in IBS diarrhea(IBS-D) patients compared to healthy individuals or patients with ulcerative colitis. When diarrhea is the major complaint, the possibility of lactase deficiency, laxative abuse, malabsorption, celiac sprue, hyperthyroidism, inflammatory bowel disease, and infectious diarrhea must be ruled out.

IV. Management :

A careful history and physical examination are frequently helpful in establishing the diagnosis. Pain due to IBS that occurs in the epigastric or periumbilical area must be differentiated from biliary tract disease, peptic ulcer disorders, intestinal ischemia, and carcinoma of the stomach and pancreas. Intestinal infestation with Giardia lamblia or other parasites may cause similar symptoms. In contrast, constipation may be a side effect of many different drugs such as anticholinergics, antihypertensive, and antidepressant medications. Endocrinopathies such as hypothyroidism and hypoparathyroidism must be considered in the differential diagnosis of constipation.

Antidepressant drug: the tricyclic antidepressant imipramine slows jejunal migrating motor complex transit propagation and delays orocecal and whole-gut transit, indicative of a motor inhibitory effect. In contrast to tricyclic agents, the selective serotonin reuptake inhibitors (SSRI) paroxetine accelerates orocecal transit.SSRI citalopram reduces the magnitude of the gastrocolonic response in healthy volunteers.
Anti flatulence therapy: avoiding flatogenic foods, exercising, losing excess weight, and taking activated charcoal are safe but unproven remedies.
Serotonin receptors agonist and antagonists: serotonin receptor antagonists. In humans, a 5-HT3 receptor antagonist such as alosetron reduces the perception of painful visceral stimulation in IBS.
Chloride channel activators: Lubiprostone is a bicyclic fatty acid that stimulates chloride channels in the membrane of intestinal epithelial cells. This drug induces passive movement of sodium and water into the bowel lumen and improves bowel function. The major effects are nausea and diarrhea.