Transcript
A (0:00)
Welcome back to Run the List, a medical education podcast in internal medicine. As a quick disclaimer, this podcast is made for educational and informational purposes only and should not be understood as medical advice under any circumstances.
B (0:28)
I am Ali Shebe, a current third year medical student at Harvard and a recent member of the RTL team. Today we will be talking about small intestinal bacterial overgrowth, also known as sibo, an increasingly discussed and diagnosed condition in the primary care office and gastroenterology clinic. I have with me Dr. Kumar, a gastroenterologist at Brigham and Women's Hospital and of course women of our fearless leaders of rtl.
C (0:54)
Thank you so much Ali. It's so great to be back recording with you and especially on such a hot topic as sibo. I also want to thank you for all your outstanding work in bringing back our RTL handouts along with your co medical student Hannah Shapiro, who is also a third year student at Harvard Medical School. And if I may have the honors, it's been a little bit, so I'd love to say our token line here. Let's go ahead and run the list.
B (1:19)
And as always, let's start with the case. Ms. R is a 45 year old female with a history of obesity status post roux en y gastric bypass who presents to primary care clinic with two months of worsening bloating, flatulence and diarrhea. She reports abdominal distension, is present upon waking up and worsens after meals. She's concerned that she might have underlying SIBO. Dr. Kumar, can you first explain what SIBO is?
C (1:48)
Absolutely. So sibo, or small intestinal bacterial overgrowth, is a condition in which bacteria proliferate in the small intestine which would otherwise be a largely sterile environment where you do not have very much bacteria at all. So we can contrast that with the colon, which is full of bacteria, and think about how if these bacteria or other species take residence by more proximally in the small intestine, how those bacteria can produce a variety of symptoms. For patients dealing with this condition, that totally makes sense.
B (2:19)
So how does the overgrowth of bacteria cause the symptoms our patient is experiencing?
C (2:24)
That's an excellent question, Ali. And the way I think about this when I'm teaching or even when I'm in clinic and talking to my own patients, is that there's three main pathways for bacterial overgrowth of a small intestine to cause symptoms. So the first one is that the small intestinal bacteria that are in this area of the digestive tract where they shouldn't be end up breaking down the foods and the nutrients from a recently ingested meal. Right, because the first thing that happens after the food empties from the stomach is that it gets into the small intestine. And normally those nutrients would be broken down and completely absorbed in the small intestine. But when there's bacteria there, the bacteria actually break down these nutrients and. And in the process of breaking down these products, they release gas. And that gas leads to the classic symptoms of abdominal bloating, cramping, distension, as well as flatulence. So the first mechanism is from the bacteria breaking down the food products and releasing gas. Now, the second pathway that I think about is how these small intestinal bacteria, which again, are not in the location that they should be, they can actually take up resonance right along the mucosal surfaces of the small intestine. And as they line up on the mucosal surfaces, they can interfere with absorption. In these cases, what typically happens is a watery diarrhea ensues because the unabsorbed substances that would have otherwise been absorbed, but instead are remaining in the lumen because they're not getting absorbed, being blocked by the bacteria that are line of mucosa. Those unabsorbed substances draw water into the intestinal tract, a la osmotic diarrhea. So in even more severe cases, you don't only have an osmotic diarrhea, but you can also get steatorrhea because small intestinal bacteria actually disrupt absorption of fats. So some patients with SIBO actually complain more of steatorrhea where they see oil droplets in the stool, or they have the classic very difficult to flush stool from the toilet bowl of statorrhea. So think about what is happening at the mucosal level in terms of absorption and how that can lead to osmotic as well as statorrhea and the third pathway, and this is typically only in extreme cases, but these same small intestinal bacteria that are competing for nutrients and potentially interfering with absorption at the level of the mucosa, they can actually lead to vitamin and mineral deficiencies. So what can happen is that these bacteria can absorb B12 for themselves and take that away, essentially steal it from the host and cause B12 deficiency. This can also happen with iron deficiency as well, where the bacteria are consuming the iron that was ingested, and instead of the host being able to absorb that iron, the bacteria take it for themselves. And then inversely, an interesting phenomenon is that some of these bacteria actually produce folate, and so they can raise the levels of folate above assay when measured from the blood. So a little pearl to share is that if you have a patient who has clinical signs or symptoms of sibo, let's say they have the abdominal gas, distension and diarrhea. You may also see this hallmark sign on labs where they have B12 deficiency because the SIBO is stealing the B12 from the host. And then high folate levels, often greater than assay because they are producing folate. So I always, if the patients happen to have had recent anemia, labs with a B12 and folate, I look to look at those because it fits that pattern. Low B12, high folate. I'm thinking, okay, my index of suspicion for this being sibo is even higher.