How do you spell relief for irritable bowel syndrome?
Many treatment options lack strong evidence for their efficacy. Others have proven efficacy, but restricted use.
A second study from the same group demonstrated that 84% of 111 consecutive IBS patients had small intestinal bacterial overgrowth compared with 20% of healthy controls. Thirty-five percent of the IBS patients treated with neomycin had improved composite scores compared with 11.4% of those receiving placebo.15
Correlation between small intestinal bacterial overgrowth and Rome criteria for IBS has not been replicated by other centers, and other investigators who have looked into this relationship have suggested that small intestinal bacterial overgrowth is not associated with IBS.16,17
Genetics and the environment may also be at work
Familial clustering of IBS is commonly seen.3,18 Several studies have suggested a genetic role but a recently published comprehensive review suggests that the evidence of genetic susceptibility to IBS is modest, if present at all.19
The discovery of physiological differences between IBS patients and control groups suggests that IBS entails significant underlying neuroenteric dysfunction wherein both function and physiology are altered.4,5 The endogenous release of serotonin (5-HT) initiates sensory, secretory, and motor signals within the enteric nervous system by binding to a variety of serotonergic receptors as well as stimulating afferent signals to the spinal cord and brain.4,6,7
Studies by multiple groups using human subjects or human tissue demonstrate physiologic differences between IBS patients and controls which include:5,7
- increased enterochromaffin cell numbers, specifically in post-infectious IBS
- a decrease in mRNA for TPH-1, an enzyme that synthesizes 5-HT
- significant differences in the 5-HT content of enterochromaffin cells
- decreased expression of the serotonin reuptake transporter protein that helps regulate serotonin signaling.
Significant disruption of 5-HT signaling is found in IBS patients compared with controls and more work is underway to better understand the relationship between physiologic dysfunction and symptoms.
Research tells us that the environment also plays a role; specifically, psychological stress is related to IBS symptoms. In one GI referral practice, women with diagnoses of functional disorders had experienced a high frequency of abuse.20
Abuse history is also associated with more severe symptoms, worse daily function, greater psychological distress, and poor health outcome.21 Removal of these stressors provides significant relief to the patient, but IBS still exists in the absence of significant psychosocial pressures.
Few tests (if any) are needed for diagnosis
IBS historically has been a diagnosis of exclusion, but this is no longer the case. You can make the diagnosis with few—if any—diagnostic tests, as long as there are no “red flag” findings or alarm symptoms (TABLE 21,22,23). In particular, surgery is not required to make a diagnosis, nor will it improve a patient’s condition, yet the incidence of abdominal and pelvic surgery in IBS patients is 87% greater, and cholecystectomy three-fold higher, than in the general population.24
While taking a history, you will of course ask about the patient’s altered bowel habits. In addition, though, you will need to:
Ask about personal and family history of inflammatory bowel disease (IBD), colon cancer, celiac disease, pregnancy, recent overseas travel or camping exposure to parasites or contaminated food and water, and history of recent gastroenteritis.25
Ask about alarm symptoms and red flags. Red flags on your examination include any focal positive physical findings, such as peritoneal signs, heme-positive stool, abdominal mass, or pelvic findings. Alarm symptoms that the patient may talk about include things like significant weight loss.
Red flags are based on observational data but have become the accepted standard of practice.1,22,23,26 Extensive testing, including the routine use of blood tests, stool studies, and imaging, however, is not required.22,25 If you have any doubt about history or findings, your diagnostic testing should focus on the issue in question.
When warranted by the presence of alarm symptoms or family history, you may need to schedule a colonoscopy to rule out IBD, tumors, or melanosis coli, which can be caused by excessive use of laxatives. Screening colonoscopy is the standard of care for all patients older than 50, regardless of symptoms.
Key in on food concerns. If specific foods aggravate symptoms, further investigation or a dietary exclusion trial may be helpful; however, even patients with proven lactase deficiency experience little or no bloating after drinking 240 mL milk.1,27 You may want to test for celiac disease if indicated by clinical features such as diarrhea, local prevalence, or family history. Routine testing of celiac disease, however, is not supported by the evidence.28,29
