Irritable bowel syndrome (IBS) is the most common of the functional gastrointestinal disorders (FGIDs).1 A recent review has shown that the mean prevalence of IBS varies widely, ranging from 1.1% in Iran and France to 35.5% in Mexico.2,3 However, different reports on IBS frequency in the Iranian population revealed that the prevalence of IBS is between 1.1 and 25%. The wide discrepancy may be due to differences in population cohorts or inconsistency in socioeconomic and cultural status.4

Colonoscopy is not a routine diagnostic modality in IBS. The British guidelines do not suggest routine colonoscopy in adults that meet the IBS diagnostic criteria.5 Likewise, the American College of Gastroenterology does not recommend routine colonoscopy in patients under 45 years of age, with IBS symptoms and no alarm signs.6 Recent clinical trials in patients fulfilling the Rome III criteria, with no alarm features, have shown that a positive diagnostic strategy with limited blood tests is similar in safety, compared with a rule-out strategy that employs extensive laboratory testing and sigmoidoscopy.7 However, most patients with symptoms consistent with IBS and warning signs are referred for colonoscopy, to rule out organic diseases, such as inflammatory bowel disease (IBD) and colorectal cancer (CRC).8

To the best of our knowledge, there have been no studies comparing colonoscopy findings and mucosal lesions in IBS patients and controls in Iran. The aim of the present study was to compare organic lesions between IBS and non-IBS patients.

Of the 208 patients, 11 were excluded due to a history of severe congestive heart failure and oliguric renal failure. The IBS group included 96 patients, the majority of whom were males (55.2%), with a mean age in years (± SD) of 43.23 (± 12.69). Of the 101 patients in the non-IBS group, 63.3% were females, with a mean age in years (± SD) of 47.66 (± 14.11). There was no significant difference in mean age between the two groups (p=0.595).

The main indications for colonoscopy in the IBS group were abdominal pain, rectal bleeding with fresh blood, and a positive fecal occult blood test. Patients in the non-IBS group mainly underwent colonoscopy due to rectal bleeding with fresh blood, CRC surveillance, and abdominal pain (Table 1).

The most common macroscopic findings in the colonoscopy reports of the two groups were hemorrhoids, polyps, and fissure, respectively (Table 2).

The normal/total percentage of biopsies taken from the IBS and non-IBS groups were 71/89 (79.7%) and 33/58 (56.8%), respectively. Table 3 shows the frequency of pathologic biopsies in both groups. No statistically significant difference was observed between the groups, regarding the prevalence of polyps.

Since the 1980s, various symptom-based criteria have been developed by gastroenterologists, for diagnosing IBS. Those criteria aim to decrease extensive and unnecessary testing for making the IBS diagnosis. The Rome IV criteria were introduced in 2016 and are now the gold standard for diagnosing IBS.10 In that setting, the physician needs to consider alarm features and rule out selected organic diseases. Important alarm features are symptom onset after 45 years of age, severe or worsening abdominal pain or other recent symptoms, rectal bleeding with fresh blood or melena, unexplained weight loss, nocturnal symptoms, iron deficiency anemia, and a family history of specific structural diseases, such as CRC, IBD, or celiac disease.

Further evaluation of individuals presenting with alarm features is recommended, particularly through colonoscopy.3,11,12 About one-third of individuals suffering from IBS are estimated to undergo colonoscopy during their clinical assessment.13 Notably, most diagnostic evaluations eventually have a negative result, and additional work-up rarely changes the diagnosis in patients meeting the Rome criteria.14 Thus, it is crucial to have negative clinical and paraclinical results in patients with warning signs.12 Lieberman et al. reported that IBS evaluation was one of the most common reasons for performing colonoscopy in patients<50 years of age.15

Undiagnosed underlying IBD is a matter of concern in IBS cases. We found that only 1% of the IBS patients were ultimately diagnosed with IBD, and the result was the same in the controls. Differentiation between IBS and IBD can be challenging because of their shared symptoms, such as abdominal pain and a change in bowel habits. Evidence suggests that patients usually present with IBS-like symptoms before IBD diagnosis. Moreover, those symptoms are more common in IBD patients.16,17 In a prospective study comparing controls and non-constipated IBS cases, regarding the prevalence of organic colonic lesions, those authors concluded that less than 1% of the IBS patients, and none of the controls, were finally diagnosed with IBD, results that are comparable to ours. However, it should be noted that routine colonoscopy is no longer recommended in IBS patients that do not present with alarm signs. At present, IBD screening with non-invasive biomarkers may be justified and practical. For instance, measuring the fecal calprotectin level can predict intestinal inflammation and is cost-effective and beneficial in adults.18 The fecal calprotectin cutoff level of<40μg/g and C-reactive protein cutoff level of<0.5mg/dl can rule out IBD in IBS patients. Likewise, the addition of fecal calprotectin and CRP may enhance the reliability of IBS symptom-based diagnoses.19

Missing CRC in IBS patients is always a major concern at the healthcare services. In the present study, neither the IBS patients nor the controls were finally diagnosed with CRC. That result is consistent with the data in previously published articles. In a recent case-control study in Taiwan, IBS did not increase the incidence of CRC, during 10 years of follow-up. However, there was a notable exception to that general pattern during the first 2 years, especially in the first 3 months, when a significant association was observed between IBS and CRC.20

Similarly, a study in Denmark revealed no significant association between IBS and CRC over a decade of follow-up, except in the first 3 months.21 In a similar population-based investigation, Rodriguez et al. concluded that the increased risk of CRC was observed only in the first year after IBS diagnosis.22 There appears to be a strong and positive correlation between IBS and CRC, within the first year of IBS diagnosis. The similarity of colon cancer symptoms to IBS symptoms has been suggested to possibly lead to primary IBS misdiagnosis.20,22

CRC is the third most commonly occurring cancer worldwide.23 Approximately 80% of CRC develops from chromosomal instability. Adenomatous polyps are considered primary lesions that are eventually transformed into CRC by extensively alternating chromosomes, aberrantly activating growth-promoting pathways, and suppressing apoptosis.24 Adenomatous polyps may progress to cancer over 10, or even 15, years.25 In our study, the prevalence of adenomatous polyps in the right colon of the non-IBS patients was higher, compared with the IBS patients. The progression to CRC of proximal polyps or large adenomas (≥ 20mm) has also been shown to be significantly higher, compared with the general population.26 Polyp distribution was similar in the transverse and left colon of patients in our two study groups. Interestingly, similar research results have indicated that the prevalence of several polyps in IBS patients is lower than in controls.15,27 In summary, the present study demonstrated that the prevalence of organic colonic lesions in the IBS patients and the non-IBS patients was in the same range. It should be underlined that the predictive value of the Rome IV criteria for diagnosing IBS is acceptable. Further evaluation via colonoscopy in IBS should be based on the presence of alarm features.

In conclusion, to the best of our knowledge, this is the first study to evaluate organic lesions in the Iranian population. We compared colonic lesions in IBS and non-IBS patients that underwent colonoscopy examinations. We found that the prevalence of structural lesions of the colon in patients meeting the Rome IV criteria was not noticeably different from that in other patients. The present result emphasizes the acceptability of the predictive value of the Rome IV criteria for diagnosing IBS.

This study was part of a thesis submitted to the school of medicine. The vice chancellor for research at the Shiraz University of Medical Sciences financially supported the study (grant No. 1397-01-01-17970).

The authors declare that there is no conflict of interest.