Bacterial Overgrowth Flashcards
Bacterial Overgrowth - Ix
The gold standard investigation of bacterial overgrowth is small bowel aspiration and culture
Other possible investigations include:
hydrogen breath test
14C-xylose breath test
14C-glycocholate breath test: used increasingly less due to low specificity
In practice many clinicians give an empirical course of antibiotics as a trial
Bacterial Overgrowth
Bacterial overgrowth affects the small intestine, and by definition is diagnosed by jejunal aspirate revealing the presence of >105 bacteria/ml. It often presents with non-specific abdominal symptoms such as nausea, abdominal pain, bloating, diarrhoea, steatorrhoea and weight loss. It also presents with symptoms of malabsorption of various nutrients. Predisposing factors include anatomical disturbances of the intestine (such as fissuring and strictures secondary to Crohn’s disease) dysmotility and various medications such as proton pump inhibitors.
Bacterial Overgrowth - Example Question
A 42-year-old lady with known longstanding Crohn’s disease was referred to the gastroenterology clinic. She presented to her GP with an 8-month history of tiredness. Since then she has developed loose stools with vague persistent abdominal pains with bloating and weight loss of approximately 4kg over the corresponding period. Her symptoms were initially attributed to irritable bowel syndrome but despite a trial of mebeverine 135mg TDS and loperamide 2mg PRN her symptoms persisted. She stated that her Crohn’s disease was well controlled for several years with mesalazine 500mg TDS. In addition to Crohn’s disease, she also had a past medical history of asthma and eczema for which she was prescribed mesalazine, Clenil modulite 200mcg BD, salbutamol PRN and Diprobase cream. She consumes 28 units of alcohol per week and is a non-smoker.
On examination, she appeared pale but otherwise well. She had a temperature of 37.3ºC, a heart rate of 88/min and a blood pressure of 122/78 mmHg. Examination of the cardiovascular and neurological system was unremarkable. Examination of the gastrointestinal system likewise was unremarkable with no organomegaly and a soft non-tender abdomen.
Investigations revealed the following results:
Hb 86 g/l MCV 112 fl Platelets 342 * 109/l WBC 7.2 * 109/l TSH 1.96 u/l B12 64 ng/l (160-900) Folate 28 mcg/l (3-20)
Gastroscopy: normal appearance
Colonoscopy: normal appearance
Capsule endoscopy: jejunal strictures and fistulae
Schilling test: Prior to administration of intrinsic factor 1% B12 isotope excreted
Post-administration of intrinsic factor 1% B12 isotope excreted
What is the most likely diagnosis?
> Bacterial overgrowth Blind loop syndrome Pernicious anaemia Terminal ileal disease Vegan diet
The schilling test here shows an initial abnormally low excretion of B12 isotope which is not normalised by administration of intrinsic factor, excluding the presence of an intrinsic factor deficiency. This lady has presented with chronic malabsorptive symptoms and a macrocytic anaemia. The capsule endoscopy did not reveal any ileum disease and in this context, the most likely diagnosis is one of bacterial overgrowth.
Bacterial Overgrowth - Example Question
A 60-year-old lady comes to clinic for review. She feels tired and lethargic and complains of loose stools for the past two months. She feels bloated and admits to losing a considerable amount of weight recently. She tells you she must be very dehydrated because her skin has become quite tight and inelastic.
Her notes mention a recent colonoscopy which showed diverticulosis but no polyps or inflammation. Upper GI endoscopy was unremarkable.
Her blood tests are as follows:
Hb 101 g/l Platelets 198 * 109/l WBC 8.3 * 109/l MCV 104 fL CRP 6 mg/l Vitamin B12 122 ng/l Folate 27 ng/l Anti-tissue transglutaminase negative
Which of the following is the most appropriate investigation?
Urea breath test > Hydrogen breath test MRCP CT colonography Anti-gliadin antibodies
This lady has a mild macrocytic anaemia, Whilst there are many causes of vitamin B12 malabsorption, it is interesting to note that the serum folate is somewhat raised. The human gut can assimilate folate synthesised by bacteria colonising the small bowel (see link below). A further clue is the tight skin, raising the possibility of scleroderma. Together these point towards small bowel bacterial overgrowth, which can be diagnosed using a hydrogen breath test.
The urea breath test is used to investigate H. pylori in the stomach.
Small Bowel Bacterial Overgrowth - Gold standard Ix - Example Question
A 34-year-old woman is seen regularly in gastroenterology clinic. She has suffered from severe epigastric pain and heartburn after eating for many years, however her OGD and pH manometry studies were both normal. She also suffers from significant bloating and crampy lower abdominal pain, with episodic loose stool. She has been diagnosed with IBS and functional dyspepsia, and is being treated with a trial of an exclusion diet and PPI, which has partially improved her symptoms. On review, she reports 4 months of worsening nausea, bloating and steatorrhoea.
You suspect that she may have developed small bowel bacterial overgrowth. What is the gold standard diagnostic test?
OGD with biopsies Stool culture D-xylose breath test > Jejunal aspirate Hydrogen breath test
Small bowel bacterial overgrowth is characterised by nausea, bloating, malnutrition and diarrhoea. There are certain risk factors for developing small bowel overgrowth, including motility disorders (including IBS), immune suppression and inflammatory bowel disease.
The gold standard diagnostic investigation is a jejunal aspirate of more than 100,000 bacteria per ml. The D-xylose test can detect malabsorption
Malabsorption caused by a problem with the small bowel mucosa can be detected by a test called the D-xylose test. Xylose is a sugar that does not require enzymes to be digested. Patient’s drink a set volume of D-xylose, and then levels of D-xylose are measured in the blood and urine. If no D-xylose is present that the small bowel is not absorbing properly, and it is not a problem of enzymatic function.
The hydrogen breath test involves measuring expired hydrogen and methane after drinking a glucose based drink. In small bowel bacterial overgrowth syndrome the sugar is not absorbed, and is then used as a metabolite for the bacteria, which produces hydrogen and methane. It compares well to jejunal aspirate, but is not the current gold standard investigation.
SBBOS - Small Bowel Bacterial Overgrowth Syndrome
= a disorder characterised by excessive amounts of bacteria in the small bowel resulting in GI Sx
RFs for SBBOS:
- Neonates w congenital GI abnormalities
- Scleroderma
- DM
It should be noted that many of the Fx overlap with IBS
- Chronic diarrhoea
- Bloating, Flatulence
- Abdo pain
Diagnosis:
- Hydrogen Breath Test
Mx:
- Correction of underlying disorder
- Abx therapy: RIFAXIMIN is now the treatment of choice due to relatively low resistance
Co-amoxiclav and Metronidazole are also effective in majority of patients
Small Bowel Bacterial Overgrowth
Small bowel bacterial overgrowth is characterised by nausea, bloating, malnutrition and diarrhoea.
There are certain risk factors for developing small bowel overgrowth, including motility disorders (including IBS), immune suppression, inflammatory bowel disease, Scleroderma
The gold standard diagnostic investigation is a jejunal aspirate of more than 100,000 bacteria per ml. The D-xylose test can detect malabsorption
Malabsorption caused by a problem with the small bowel mucosa can be detected by a test called the D-xylose test. Xylose is a sugar that does not require enzymes to be digested. Patient’s drink a set volume of D-xylose, and then levels of D-xylose are measured in the blood and urine. If no D-xylose is present that the small bowel is not absorbing properly, and it is not a problem of enzymatic function.
The hydrogen breath test involves measuring expired hydrogen and methane after drinking a glucose based drink. In small bowel bacterial overgrowth syndrome the sugar is not absorbed, and is then used as a metabolite for the bacteria, which produces hydrogen and methane. It compares well to jejunal aspirate, but is not the current gold standard investigation.
