Visceral Hypersensitivity and IBS

If you experience visceral hypersensitivity, it means you have a lowered threshold for abdominal pain and discomfort in response to pressure, stimulation, or distension within the abdomen. Visceral hypersensitivity (visceral hyperalgesia) is the term used to describe the experience of pain within the inner organs (viscera) at a level that is more intense than normal.

Visceral hypersensitivity is a hallmark characteristic of irritable bowel syndrome (IBS). However, visceral hypersensitivity may also be present in people who have:

• Non-cardiac chest pain
• Functional dyspepsia
• Functional abdominal pain

Measuring Visceral Hypersensitivity

Researchers study visceral hypersensitivity to try to understand why people have IBS. For research purposes, visceral hypersensitivity is commonly measured using a balloon distension test. This tests the response of the patient to pressure within the rectum.

In the balloon distension procedure, a balloon is inserted into the rectum and slowly filled with air. Individuals are characterized as having visceral hypersensitivity when they report pain at lower levels of pressure than others who can withstand more significant air inflation without reporting discomfort. In such research studies, people who have IBS typically experience a lower pain threshold.

Visceral Hypersensitivity and IBS

Although visceral hypersensitivity is seen as integral to IBS, only approximately 30-40% of people who have IBS have been found to have an exaggerated sensitivity to distension within the colon. And, interestingly, there is not necessarily a direct correlation between this enhanced sensitivity and the severity of a person's IBS symptoms.

It appears likely that the visceral hypersensitivity seen in some IBS patients as a result of changes in nervous system functioning on both the level of the intestines and the brain. In such cases, the nerve pathways in the gastrointestinal tract become sensitized to stimulation, resulting in over-reactivity and resulting in pain amplification.

In individuals who do not have IBS, rectal distension triggers a response in parts of the brain that are associated with modulating pain. In IBS patients, this same rectal stimulation triggers a response in the parts of the brain associated with vigilance and anxiety—parts of the brain that serve to amplify the sensation of pain.

Causes of Visceral Hypersensitivity

Once visceral hypersensitivity was established as a key component in IBS, researchers have turned their attention as to why that might be as a way to better understand the confusing nature of IBS.

There are various theories behind the experience of visceral hypersensitivity in IBS. Many factors are being investigated, including:

• Pain is arising from nerves of the cells lining the large intestine
• Changes to micro RNA molecules of these cells
• Changes in neurotransmitter and other receptors within these cells
• Changes in the interactions between the central nervous system (brain and spinal cord) and the peripheral nervous system (pathways to and from organs and muscles)
• Increased intestinal permeability (leaky gut)
• Inflammation (at a level below that which can be seen through diagnostic testing)

A better understanding as to how these complex systems interact will allow for the development of medications that will target the areas of dysfunction and bring about relief from IBS symptoms.