Irritable bowel syndrome (IBS) is one of the most common gastrointestinal disorders. Its prevalence in the general population is approximately 5%–20%, and the condition is more common in women and young adults [1]. Despite IBS being one of the most frequent reasons for consultation, many patients are misdiagnosed owing to a lack of reliable biomarkers or endoscopic findings. Endoscopic evaluation, which is performed to exclude other etiologies, is normal in more than 50% of cases. Further evaluation is not recommended for gastrointestinal functional disorders, and clinical diagnosis based on the Rome IV criteria is necessary in such cases [2].

IBS is characterized by chronic or recurrent abdominal pain associated with changes in bowel frequency and consistency. Functional abdominal pain is not associated with physiological events and cannot be fully explained by other medical conditions. Previous studies have demonstrated that the presence of Rome IV criteria, in the absence of red flags, exhibit a sensitivity and specificity of 62.7% and 97.1%, respectively [3]. However, Rome IV criteria can be present in other organic or functional gastrointestinal disorders, and it is possible that patients could be misdiagnosed as having IBS, especially when the presenting symptom is unresponsive to treatment.

Capsule endoscopy (CE) is a diagnostic method that enables visualization of the small bowel lumen and can diagnose lesions not previously detected by other methods [4]. Several studies have demonstrated that CE is superior to barium follow-through, push enteroscopy, and computed tomography for the diagnosis of small bowel disease [5-7].

The aim of this study was to evaluate the diagnostic yield and clinical impact of CE in patients with refractory diarrhea- predominant IBS (D-IBS) and functional abdominal pain.

A total of 216 medical records were evaluated by two gastroenterologists for inclusion and exclusion fulfillment criteria. Sixty-five patients (30%) were included for analysis. Another gastroenterologist, blind to the medical records and also an expert in CE, reviewed the images. The mean age was 50.2 years, and 35 (53.8%) participants were female. The main presenting symptom was diarrhea in 22 patients (33.9%) and abdominal pain in 43 patients (66.1%). The mean level of fecal calprotectin in the abdominal pain group was 18.2±6.4 and 25.3±9.2 for the D-IBS group. Demographic characteristics in both groups are summarized in Table 1.

In 28 patients (43%), findings were detected during CE. Clinically significant small bowel pathologies were identified in 26 patients (40%) (p-value=0.117), with a clinical impact of 92.8%. Inflammatory lesions and villous atrophy were the most frequent lesions found in 16.9% and 15.3% of patients, respectively.

Clinically significant lesions detected by CE were noted in 12 patients (54.6%) in group A (n=22). Villous atrophy and Crohn’s disease-related ulcers were observed in 4 (18.2%) and 8 (36.4%) patients, respectively. Normal study findings were noted in 10 patients (45.4%).

Clinically significant lesions were detected in 14 patients (32.5%) in group B (n=43). Non-specific erythema was detected in 2 patients (4.7%); however, these cases were not considered clinically relevant. Ascariasis was identified in 1 patient (2.3%) (Fig. 2A). Ulcers detected during CE (Fig. 2B) were biopsied in follow-up enteroscopy, and Crohn’s disease was diagnosed in 11 cases (100%). Villous atrophy confirmed by biopsy supported the diagnosis of celiac disease in 10 cases (100%). The submucosal tumor detected by CE was a gastrointestinal stromal tumor confirmed by histopathology (Fig. 2C). Villous atrophy was detected by CE in the jejunum (Fig. 2D). Three gastroparesis cases (6.9%) were suspected due to a prolonged time for CE passage through the small bowel and the presence of food despite the fasting protocol before CE intake and prokinetics administration. These cases were confirmed by scintigraphy. The distribution of findings detected during CE are described in Table 2.

Patients with D-IBS and functional abdominal pain diagnosis might be challenging, especially in patients with no response to medical treatment. This study evaluated the diagnostic yield and clinical impact of CE for detecting small bowel pathologies among these groups of patients.

Current diagnostic methods fail to obtain an adequate diagnosis. No specific findings discriminate IBS from healthy control patients [1]. Two trials reported a 10%–14% incidence of mucosal breaks observed via CE in healthy controls, whereas another two trials detected normal mucosa in control patients [8-11]. On the other hand, there are some suggestions that organic gastrointestinal disorders (inflammatory bowel disease, colorectal cancer, or infectious diarrhea) can be identified in subsets of patients who fulfill Rome IV criteria for IBS [12].

Although IBS diagnoses were based on Rome III criteria in this study due to the time frame of patients’ enrollment, currently available Rome IV criteria had a comparable sensitivity and specificity to that reported for Rome III [3].

CE has become an important method in the diagnosis of small bowel pathologies [13], including occult gastrointestinal bleeding, Crohn’s disease, celiac disease, inherited polyposis syndromes, and small bowel tumors [13-18].

Chronic diarrhea and abdominal pain are indications for CE. Current data suggest that CE should not be the first-line diagnostic test [19,20]. Song et al., demonstrated the positive diagnostic yield of CE (42.9%) in patients with chronic diarrhea, in whom the final diagnosis changed in 31.4% of patients, with Crohn’s disease being the most common finding [21]. In a systematic review of CE and unexplained chronic abdominal pain, a limited diagnostic yield of 20.9% was described. Inflammatory lesions were the most common bowel pathologies identified by CE (78.3%); however, increased heterogeneity between studies was found [22].

CE should be used when an organic disease is suspected or in the presence of alarm features. In patients with abdominal pain associated with weight loss, fever, anemia, positive stool guaiac test, or signs of inflammation, the possibility of detecting findings on CE increases from 18% to 41.7% [22,23].

Ohlsson et al., demonstrated that in 26% of patients with IBS-small bowel pathologies, findings can be observed when using CE [12]. However, they did not identify macroscopic abnormalities that could explain the symptoms in the majority of patients with IBS and concluded that routine use of CE in patients with IBS should not be recommended. Furthermore, they considered that a subgroup of patients initially classified with IBS with persistently severe or aggravating symptoms should undergo further investigation with CE [12]. Kalla et al., evaluated patients with D-IBS using CE and identified evidence of subtle mucosal changes in 30% of patients [24].

The present study revealed that 54.5% and 32.5% of cases unresponsive to medical treatment in groups A and B, respectively, exhibited clinically relevant pathological findings on CE.

In the present cohort, CE had an important clinical impact in 26 cases (40%), changing the clinical management of these patients.

There were some limitations in the present study. Namely, it was a retrospective, non-randomized, single-center study with no controls. Additionally, all CE images were evaluated by one expert.

In conclusion, CE had a favorable diagnostic yield and clinical impact on the management of patients with D-IBS and functional abdominal pain unresponsive to medical treatment. Routine use of CE in IBS patients should not be recommended. However, in patients with a lack of response to appropriate medical treatment, CE may identify abnormalities, thereby improving medical management.