(USMLE topics) IBS: Prevalence, signs and symptoms, types of IBS, pathophysiology, different possible causes and mechanisms, diagnosis and treatments. This video is available for instant download licensing here: https://www.alilamedicalmedia.com/-/galleries/narrated-videos-by-topics/digestive-diseases/-/medias/f68d8c06-a08a-4785-a8ae-a0110567a286-irritable-bowel-syndrome-ibs-narrated-animation
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Irritable bowel syndrome, or IBS, is the most commonly diagnosed gastrointestinal disorder, affecting at least 10% of the global population. IBS is characterized by chronic or recurrent abdominal pain, associated with a change in bowel habits. Most patients can be classified, according to their predominant stool pattern, into IBS with diarrhea, IBS with constipation, or mixed-stool IBS, in which diarrhea alternates with constipation. Other symptoms may include mucus in stools, bloating, gassiness, and feelings of severe illness. IBS symptoms can be triggered by certain foods, stress, and often get worse around menstrual periods in women. People with IBS are also likely to have other disorders such as fibromyalgia, major depression, or chronic fatigue syndrome.
IBS occurs more frequently in young adults, and affects more women than men.
IBS is a functional disorder, meaning the bowel does not function properly, but there is no observable structural damage. It is thought to associate with problems in the communication system between the gut and the central nervous system, known as the gut-brain axis. This system not only ensures proper functions of the digestive system, but also adapts digestive activities to the body’s different physiological states. Basically, sensory nerve endings in the gut transmit information about the intestinal environment to the brain. The brain integrates this information with inputs from the rest of the body, and sends back neural and hormonal signals to control various gut activities. For example, intestinal muscle contraction is regulated so that the bowel moves food at an optimal pace, allowing the body to reabsorb the right amount of water and nutrients before stools can form.
IBS patients often have irregular intestinal motility patterns. When food moves too fast through the intestine, less water is reabsorbed and stools become more watery. When food moves too slowly, more water is reabsorbed and constipation results. Sensory nerve endings in the bowel of IBS patients are also more sensitive, or “irritated”, producing the sensation of pain. This is known as visceral hypersensitivity.
IBS is classified as a syndrome, meaning a group of symptoms, rather than a single disease. This is because distinct underlying mechanisms may drive disease progression in different groups of patients. Several possible mechanisms have been identified. These include:
- alterations in brain function caused by psychological trauma, anxiety, or stress;
- intolerance to certain foods, such as short chain carbohydrates, gluten, dairy products;
- post-infectious changes, such as low-grade inflammation or altered intestinal permeability;
- disturbances in the gut microbiota;
- abnormalities in serotonin metabolism;
- and genetics.
It is common for IBS to result from a combination of several of these factors.
Diagnosis is based on symptoms, but tests are done to exclude other more serious conditions such as inflammatory bowel disease and cancers. The latest diagnostic criteria (Rome III criteria) include: abdominal pain or discomfort lasting at least 3 days a month in the last three months, associated with at least two of three factors: relief upon defecation, pain onset associated with a change in stool frequency, or pain onset associated with a change in the form of stool.
IBS rarely requires hospitalization and does not increase risks for colon cancers. Current treatments aim to relieve symptoms, which, in most people, can be managed with diet, and stress reduction. Severe cases may be treated with medications.