Women are twice as likely to have irritable bowel syndrome (IBS). Women are also more likely to develop a chronic painful condition like fibromyalgia. Is it coincidental that women are more likely to have irritable bowel syndrome and/or chronic pain? Probably not; a growing body of medical research is finding a strong association between these two illnesses. By connecting the dots and finding the root of these problems, scientists hope to find better treatments that can tackle both conditions with one stone.
Irritable Bowel Syndrome is just one diagnosis out of a whole series of diagnoses that are classified as Functional Gastrointestinal Disorders. Recently, the criteria for diagnosing IBS were revised by the ROME organization. These new criteria are called the ROME III criteria for IBS which reads as follows:
Irritable Bowel Syndrome is recurrent abdominal pain or discomfort at least three days per month in at least the last three months which is associated with two or more of the following:
Improvement with defecation2.Onset associated with a change in frequency of stool3.Onset associated with a change in form (appearance) of stool
In general, IBS patients are classified as primarily constipated (constipation predominate) or as primarily having diarrhea (diarrhea predominate). Other symptoms include: heartburn, difficulty swallowing, stomach upset, nausea, non-cardiac chest pain, bloating and gas.
What does all this gut stuff have to do with chronic pain? Well, those who have IBS are also known to have widespread hypersensitivity to painful stimuli hyperalgesia. Let's connect some dots.
Gut (visceral) hypersensitivity is well documented as a sign of IBS, but researchers have also documented that IBS patients have widespread temperature and pain sensitivity also. Visceral sensitivity is measured by applying rectal pressure and measuring the onset of sensation, the pain threshold, and the pain tolerance level. As expected, those with IBS react quickly and strongly to rectal pressure compared with normal folks without IBS. Temperature and pain sensitivity is measured by applying various stimuli like heat, cold, and electrical to various parts of the body. Surprisingly, those with IBS also have hypersensitivity in other regions of the body.
In particular, the lower extremities are more sensitive than the upper extremities. Scientists partially explain this by the fact that gut and lower-body nerves intermingle in the spinal cord and essentially "talk" to one another. This "cross-talk" can lead to the hypersensitivity in the gut translating into hypersensitivity in the legs.
On the other hand, that explanation does not expand far enough in order to explain the hyperalgesia in the arms, which do not share direct nervous system connections with the gut in the spinal cord. Because of this widespread, whole-body involvement, the mechanism of hypersensitivity must also involve the brain where everything connects. Now, with this new evidence, IBS has gone beyond being just a gut problem. Via the brain, IBS is linked it to other painful conditions that involve hyperalgesia, like fibromyalgia.
Not only are those with IBS more sensitive to painful stimuli, people with IBS also have difficulty controlling pain naturally through a process called "somatic pain inhibition." Applying ice to a painful area is type of somatic pain inhibition. In simple terms, the cold from the ice stimulates the brain to block the painful signals. When the brain cannot regulate painful signals, the body is kept in a state of hypersensitivity. This altered pain-inhibition mechanism in the central nervous system may be the ultimate link to many syndromes like IBS, complex regional pain syndrome, phantom pain, and fibromyalgia.
Other dots are still being connected between IBS and chronic pain. Many of these dots involve psychological factors like catastrophizing, depression, and psychological distress. Those with co-existing psychological issues are more likely to develop hypersensitivity in the bowels and a deficit in pain inhibition. The opposite scenario is also true. Those with hypersensitivity in the bowels and a deficit in pain inhibition are likely to become psychologically distressed. This vicious cycle emphasizes the powerful brain-gut interaction as epitomized by IBS.
ROME may have the final word in regards to diagnosing IBS. But in regards to chronic pain and IBS, all roads lead to the brain, the biggest "dot" of them all. This central link is the root of many so-called syndromes. The centralized mechanisms involved associate all of the syndromes in one way or another. When the central pain modulation system becomes altered in some fashion within the brain, a person, most likely a woman, is prone to develop one of the many syndromes that involve pain.
Whether the pain affects the entire body, the gut, or somewhere in between, is probably determined by a set of biological, psychological and social matters.
Regulating these issues will ultimately lead to a cure of IBS and chronic pain; once more dots are connected. Is it a coincidence that the same medications, like tricyclic antidepressants, used to treat chronic painful conditions are also used to treat IBS? Not at all, it's all connected.
"Widespread hypersensitivity is related to altered pain inhibition processes in irritable bowel syndrome"; Piche et al; Pain, 148 (2010), pg 49-58
"Central and peripheral hypersenstitivity in the irritable bowel syndrome"; Zhou et al; Pain; 2010; Epub ahead of print.