In this study, we found the etiologies of chronic diarrhea in Thai patients to be different from those in Western patients, particularly in small bowel diseases. Among chronic diarrhea with ileocolonic causes, the common causes in our cohort were infectious diseases and inflammatory bowel diseases, whereas IBD and microscopic colitis are the common causes in Western countries. In small bowel diseases, the most common cause of chronic diarrhea in our cohort was parasitic infections. Interestingly, we found no celiac disease, which is the common cause of small bowel disease in Western countries.
Similar to Western countries, our study showed that colonoscopy had high diagnostic performance in patients with chronic diarrhea. The diagnostic yield was 42.7%, which is comparable to the values reported by several previous studies (range: 10.0% to 49.5%).[3, 14-17] Furthermore, our study showed that the terminal ileum should be accessed because the diagnostic yield would have been decreased from 42.7% to 39.4% if the terminal ileum had not been intubated. Makkar, et al. reported that the diagnostic yield was 15.0% when colonoscopy was performed without ileal intubation, and the yield increased to 16.9% when performed with ileoscopy.[18]
American Society for Gastrointestinal Endoscopy guideline recommends EGD for chronic diarrhea work-up due to its potential for diagnosing celiac disease.[5, 19] However, the prevalence of celiac disease is low in Southeast Asia[20]; therefore, EGD had a diagnostic yield of only 5.9% in this study. Furthermore, all positive findings were also detected if ileocolonoscopy was performed, which means that EGD conferred no additional diagnostic benefit when combined with colonoscopy. This finding suggests that EGD should not be routinely performed to investigate chronic diarrhea in our region.
Interestingly, the involved small bowel segments causing chronic diarrhea in our cohort were at more distal segments that are unreachable by EGD. Nineteen patients with negative EGD and colonoscopy who underwent small bowel endoscopy were found to have mucosal diseases. Of those, 5 were diagnosed by push enteroscopy, 12 by balloon-assisted enteroscopy, 1 by typical VCE finding of intestinal capillariasis, and 1 by repeated stool examination. The diagnostic yield of push enteroscopy, BAE, and VCE was 22.7%, 60.0%, and 45.5%, respectively. Push enteroscopy could be considered instead of EGD when diarrhea from small bowel lesions is suspected in our region despite having the lowest diagnostic yield among the three modalities since most general gastroenterologists can perform it, and it is less invasive and less expensive than BAE. Balloon-assisted enteroscopy, which can more deeply access the small bowel compared to push enteroscopy, was reported the have a diagnostic yield of 55.0% to 73.5% in previous studies.[10-13] Similarly, the diagnostic yield of BAE in our study was 60%. It is essential to note that small bowel imaging studies could contribute to the high diagnostic yield of BAE since 17 of 20 BAE had small bowel imaging performed before BAE to localize the lesions. Furthermore, in 12 patients whose diagnoses were obtained by BAE, almost all (11 of 12) had lesion localization by small bowel imaging studies before the endoscopy. For VCE, the diagnostic yield in this study was 45%, which is comparable to previous studies.[7, 8] The major limitation of VCE is its inability to obtain tissue sampling. However, our study showed that VCE could help to guide the abnormal findings prior to BAE and exclude small bowel mucosal lesions if the results were normal.
Our study showed that small bowel imaging studies, either SBFT or CT abdomen, should be considered as a supplementary investigation to localize the lesion and guide which endoscopic modality should be performed. The diagnostic yield of small bowel enteroscopy was higher if those procedures were performed with guidance from small bowel imaging. As mentioned above, 11 of 12 positive BAE had lesions localization by small bowel imaging studies. Furthermore, a normal imaging study result could suggest non-mucosal diseases; only one of 4 patients with normal imaging had a mucosal disease.
For the predictive factors associated with the diagnosis of small bowel mucosal diseases among patients with negative EGD and colonoscopy, lower albumin level was the significant predictor in univariate analysis, and it was almost significant in multivariate analysis. This result is in accordant with the study by Song et al., which showed that hypoalbuminemia and hematochezia were significant predictive factors for a positive diagnostic yield of VCE in patients with chronic diarrhea.[7]
Based on the results of this study, we propose a diagnostic diagram for patients with chronic diarrhea in our region, as shown in Figure 3.
Strengths and limitations
The strength of this study is that it is the first to report the diagnostic performance of each endoscopic modality in chronic diarrhea in an area with a high prevalence of infections and a low prevalence of celiac disease. We also investigated the role of small bowel imaging in the diagnosis of chronic diarrhea. The most notable limitation is our study's retrospective design, which made it impossible to perform all evaluated modalities in all patients. Another limitation is that our data were collected from a single center.