SMALL INTESTINE: Edited by David S. Sanders
The history of gastroenterology is an interesting one and bears a close relationship with ‘what we eat’ and our diet. The earliest known representation of the gut is c. 30000 BC in a Paleolithic cave painting in Lascuax and depicts loops of bowel spilling out from where a spear has penetrated a bison . From there on dietary hygiene is mentioned in the Bible (c. 2500 BC Old Testament) and onwards and upwards through Egyptian, Greek and Babylonian societies . Although the gut in medicine is a continuous source of interest and investigation – contemporary gastroenterological practice has not always focussed on the small bowel. We have had phases of interest and expertise with upper Gastrointestinal (GI) (with the boom of H. Pylori in the 1980s), Inflammatory Bowel Disease, Hepatology and Endoscopy. Clinicians will declare themselves as having an expertise in any of these fields but beyond the sub-speciality of Nutrition there has been less focus on the small bowel. Why would this be? Rigid Endoscopy has been repeatedly attempted throughout history but it was the advent of fibre-optics (in the 1950s) that brought us the modern day endoscope. This is credited jointly to Basil Hirschowitz and Larry Curtiss in the United States and concurrently Harold Hopkins in the United Kingdom . However, because of its length and untethered nature the small bowel remained elusive and I would perhaps controversially suggest that Gastroenterologists of that time took an approach of ‘If I can’t see it or reach it with an endoscope then I won’t study it too closely!’.
This all changed with the advent of small bowel capsule endoscopy . Since that time there has been a revolution in small bowel imaging with more than 1.5 Million patients having swallowed the Pillcam (the current market leader of the options available) [3,4]. The financial market is projected to be almost $900 million by 2022 . With this has come renewed interest and scientific rigor towards the small bowel. Device assisted enteroscopy has augmented this further by allowing access to the small bowel for both therapeutic options and biopsy .
In this edition of Current Opinion of Gastroenterology we have selected six areas which I would contend demonstrate a coming of age for a gastroenterologist declaring themselves as having a small bowel sub-specialist interest.
Coeliac disease we have known for some time is more common and protean than we think but Lau (pp. 173–180) review the literature extending our understanding by summarising the evidence for clinicians to take a bulb biopsy to optimise the diagnosis (increased diagnostic yield of about 10%) and managing patients with a gluten free diet who have potential coeliac disease or are ‘Coeliac Lite’. Finally the clinical conundrum of antibody negative villous atrophy and how to manage it is discussed [6–8].
A small bowel endoscopy update by Ching et al. (pp. 181–188) reflects a further extension in the role of this noninvasive endoscopic modality. Whilst meta-analysis has shown its superiority over other modalities for recognition of small bowel Crohn's and in obscure gastrointestinal bleeding the recent study by Xue et al.  suggests on meta-analysis a pooled diagnostic yield of 20.6% for unexplained abdominal pain. So perhaps when conventional tests have failed and the patient is still in distress a small bowel capsule is worthy of discussion and consideration?
Both the clinical and pathophysiological evidence is presented by Oduyebo and Camilleri (pp. 189–195) for a fascinating new disease or re-recognised disease -- bile acid diarrhoea. This is the ‘hot topic’ of the moment. First a nomenclature change from bile acid malabsorption to bile acid diarrhoea (BAD) . This is crucial because BAD has significant overlap with IBS type symptoms. Although SeHCAT is not widely available in the United States, there has been significant validation of fasting serum FGF-19 and 7 α-hydroxy-cholesten-3-one (C4), a surrogate measure of bile acid synthesis Ching et al. (pp. 181–188). When these are commercially available recognition of this BAD epidemic will follow. Furthermore currently the Bile Acid sequestrants are the primary treatments for BAD but our understanding of the FXR-FGF-19 pathway provides an alternative therapeutic target for BAD.
Aziz et al. (pp. 196–202) provide an overview of the lack of a relationship between small intestinal bacterial overgrowth (SIBO) and diarrhoea predominant IBS type symptoms. This may reflect the poor quality tests we have currently to detect SIBO or because the original SIBO bacteria count on which we base our definition ×105 is fundamentally flawed as it was described in patients following surgical diversion and not healthy controls! A recent U.S. study (prospective dual centre) evaluating patients with unexplained gastrointestinal symptoms (seemingly characteristic of IBS) found there to be no difference in overall symptom scores between those testing positive against those testing negative for SIBO, when using either small bowel aspirate or glucose hydrogen breath test. Moreover there was no difference in symptom scores between IBS type patients with small bowel aspirate of more than 103 CFU/ml versus those with a count of more than 105 CFU/ml . Nevertheless the Pimentel et al.  studies have shown short-term improvement of symptoms using rifaximin. Whether this has any relationship to SIBO remains unclear and it may in fact be colonic flora which is the culprit – however rifaximin has now joined our armamentarium for IBS treatments. As Aziz concludes more work is required to clarify this controversial clinical practice for both clinicians and patients alike.
Finally I will draw your attention to small bowel transplantation and the advent of Teduglutide. Loo et al. (pp. 203–211) reiterate the importance of early referral to specialist centres for small bowel transplant consideration but reinforce that home parenteral nutrition is still the established and comparatively well tolerated option. As Oke discusses Oke et al. (pp. 212–217), in the United Kingdom this is an expensive treatment, costing between £95 and £235 per day; however, when Teduglutide becomes a more commercially viable option it will all be change again! [13,14] Who would not want to try this treatment if it works for them and is financially affordable. Freedom from parenteral nutrition or even simply reduced feeding times is a massive incentive for patients and although without an evidence base to my knowledge would be a source for patient reported outcomes were we to ask.
I would conclude by making a suggestion. In my unit we have the largest capsule service in the United Kingdom (>600 undertaken per annum) and perform nearly 75–100 device assisted enteroscopies per annum. We also provide a National Referral Centre for Coeliac Disease. There are three consultants whose specialist interest is small bowel disease. You, like me, I am sure have been watching the expansion of small bowel endoscopy nationally and internationally as well as the increasing recognition and detection of coeliac disease. Given the range and diversity of topics covered in this edition -- could you imagine that every centre requires a consultant with a small bowel interest? Perhaps it does not seem unreasonable to suggest that taken as a whole the dawn of the small bowel expert has cometh!
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