Bariatric Times

NOV 2017

A peer-reviewed, evidence-based journal that promotes clinical development and metabolic insights in total bariatric patient care for the healthcare professional

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16 Review Bariatric Times • November 2017 INTRODUCTION Bariatric surgery has been shown to promote weight loss and slow or reverse progression of comorbid conditions, such as diabetes, obstructive sleep apnea, hyperlipidemia, and hypertension, in adults and adolescents. 1,2 In comparison to restrictive bariatric procedures (gastric sleeve, gastric balloon, gastric band), the malabsorptive procedures [Roux-en- Y gastric bypass (RNYGB), jejunoileal bypass, biliopancreatic switch] are associated with greater weight loss but can also lead to idiosyncratic complications, as the creation of blind loops of the small bowel can be sites for small intestinal bacterial overgrowth (SIBO) (Figure 1). SIBO OVERVIEW The small intestine normally harbors fewer than 10 3 bacteria/mL, and SIBO is defined as small intestinal bacterial populations exceeding 10 5 –10 6 bacterial organisms/mL. SIBO develops in a variety of clinical conditions involving gastric acid suppression, disordered gastrointestinal motility, or structural abnormalities of the gastrointestinal tract, all of which are permissive for bacterial proliferation. 3 Symptoms range from diarrhea and bloating to weight loss and vitamin deficiencies, depending on the type of colonizing microorganism. No widely accepted gold standard for diagnosis of SIBO exists. 4 Bacterial culture of small bowel luminal content is the most direct test, but this method is time- consuming, cumbersome, and might underestimate bacterial populations that are difficult to culture. Clinically, measuring levels of hydrogen gas—presumably produced by anaerobic bacteria abnormally colonizing the small bowel—that are exhaled after a fixed dose of oral glucose or lactulose is the most common test for SIBO. Observing elevated breath hydrogen levels compared to fasting, or seeing two peaks in hydrogen production after the oral carbohydrate load, are considered a positive result. Diagnosing SIBO in bariatric patients is especially challenging because symptoms mimic those of bariatric surgery in general, and hydrogen breath tests can be misleading due to anatomic alterations. However, accurate identification is important in order to properly treat patients. ACCURATE DIAGNOSIS OF SIBO FOLLOWING BARIATRIC SURGERY Gastric bypass surgery results in faster small bowel transit time, such that the hydrogen breath test can be misleading if measured at a standard time after oral carbohydrate load. This is because the carbohydrate bolus might have already reached the colon, where anaerobic metabolism is normal. In one study, 19 patients with RNYGB experiencing diarrhea, bloating, flatulence, and abdominal pain underwent simultaneous lactulose breath testing to assess presence of bacterial growth and upper GI series with small bowel follow-through to assess orocecal transit time. Nine patients had positive lactulose breath test (>20ppm rise in hydrogen above baseline within 90 minutes), of whom six had orocecal transit time preceding the time to rise in exhaled hydrogen, suggesting that the measured hydrogen was produced by normal colonic flora, not bacteria abnormally colonizing the small intestine. All nine patients received oral antibiotics for presumed SIBO, but only the three with orocecal transit times exceeding the time of rise of breath hydrogen responded to treatment 5 . Thus, accurate diagnosis and appropriate treatment of SIBO in patients with nonspecific and mild symptoms might require specialized protocols in post-gastric-bypass patients. To describe more drastic presentations of SIBO, referring to historical experience with jejunoileal bypass (JIB) is illuminating. JIB AND SIBO JIB was an early form of bariatric surgery that was popular in the 1960s and 70s and has since largely been replaced by gastric bypass due to the high rate of complications, including diarrhea, vitamin deficiencies, and asthenia. 6 The exact mechanisms of all these complications remain unclear, but bacterial colonization of the bypassed small bowel might be one of the culprits. For example, experimental studies in rats have found that 90-percent small bowel resection causes 15-percent reduction in weight, while 90- percent bypass leads to twice as much weight loss. This effect can be nearly eliminated by treatment with metronidazole but not cephalexin, suggesting that bacterial overgrowth in the excluded blind loop of the small bowel might contribute to post- surgical malabsorption. 7 Besides excess weight loss, other complications of JIB thought to be related to SIBO include bypass enteritis, hypovitaminosis B12, proctitis, encephalopathy, liver disease, polyarthritis, nephrolithiasis, cholelithiasis, and dermatitis, based on the detection of bacterial antigen/antibody complexes involved in these conditions or the observation that antibiotic treatment was clinically effective in reducing symptom severity. 8 One of the most well-described SIBO-associated complication is the bowel-associated dermatosis-arthritis syndrome (BADAS), which occurs in about 6.5 percent of patients following JIB or up to one third of patients undergoing jejunocolonic bypass. 9 This condition manifests as a maculopapular rash that usually affects the trunk and arms, flu-like symptoms, polyarthralgias, and myalgias developing three months to five years after surgery. The pathogenesis of this disorder involves bacterial peptidoglycans, 10 which lead to alternative pathway complement activation, production of circulating immune complexes, IgM and IgG deposition in dermal vessels and the dermoepidermal junction, and neutrophilic extravasation into by DIANA MIAO, BA Bariatric Times. 2017;14(11):16–19. Small Intestinal Bacterial Overgrowth in Modern Bariatric Surgery ABSTRACT Small intestinal bacterial overgrowth (SIBO) is a rare complication of Roux-en- Y gastric bypass, but was relatively common following jejunoileal bypass (JIB) and can lead to severe malabsorption and serious autoimmune systemic disease. Prompt recognition of this condition can guide appropriate antibiotic therapy, thus preventing complications from chronic total protein malnutrition or vitamin and micronutrient deficiencies. Furthermore, the gut microbiome undergoes substantial changes in all patients who have undergone gastric bypass surgeries and might have a prominent role in regulating post-operative weight loss. Further research at the intersection of bariatric surgery and the gut microbiome can increase understanding of the mechanisms of weight loss following malabsorptive surgical procedures, as well as enhance clinical recognition of rare complications like SIBO that can lead to adverse patient outcomes. KEYWORDS Roux-en-Y gastric bypass, jejunoileal bypass, microbiome, SIBO

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