Small intestinal bacterial overgrowth syndrome

The place of the syndrome in the classification of dysbiosis

In clinical practice, dysbiosis is classified according to several basic principles. First, the etiological factor is taken into account: dysbiosis can be fungal, staphylococcal, proteus-induced, or caused by other microorganisms. Second, the precise localization of the pathological process is of fundamental importance. Traditionally, oral dysbiosis, vaginal dysbiosis, and intestinal dysbiosis are distinguished.

When assessing intestinal specificity, it is essential to strictly differentiate between the involvement of various segments of the digestive tract. Colonic dysbiosis is considered by clinicians separately from small intestinal pathology. Specifically, an excessive bacterial pool in the small intestine is classified as small intestinal bacterial overgrowth syndrome (Bacterial overgrowth syndrome). This condition is always inextricably linked with qualitative and quantitative changes in the microbiome.

Pathogenetic connection with therapy and liver diseases

Special attention is required to assess the risks of developing SIBO in hepatology patients. According to clinical guidelines, it is necessary to strictly restrict the prescription of proton pump inhibitors (PPIs) to patients suffering from liver cirrhosis complicated by ascites. This measure aims to prevent spontaneous bacterial peritonitis (SBP).

The pathogenetic rationale for this restriction is based on the following cascade of complications. Prolonged use of proton pump inhibitors provokes the development of small intestinal bacterial overgrowth syndrome within the lumen of the small intestine. An excess of bacterial flora leads to enhanced pathological bacterial translocation. As a result, the probability of developing spontaneous bacterial peritonitis and a severe complication — hepatic encephalopathy — increases manifold.

An important clinical clarification concerns patients with portal hypertensive gastropathy (PHG). The presence of this condition is not an indication for therapy with proton pump inhibitors. Non-selective beta-blockers should be used exclusively as the drugs of choice for portal hypertensive gastropathy.

Etiological factors and development triggers

The development of small intestinal bacterial overgrowth syndrome is associated with an extensive list of external and internal factors, which are generally divided into several key groups:

• Alimentary factors and gastrointestinal pathologies. Alimentary triggers include malnutrition, as well as rapid weight loss resulting from bariatric surgery or prolonged fasting. The connection between SIBO and total parenteral nutrition has been reliably proven. Structural and inflammatory pathologies include short bowel syndrome, celiac disease, inflammatory bowel disease (IBD), and prior pancreatectomy.
• Infectious agents. The clinical picture often shows a direct link with HIV infection, as well as with hepatitis C virus (HCV), with genotype 3 being the most specific risk factor.
• Endocrine disorders. Hormonal imbalance affects gut motility and the microbiome. This group includes hypothyroidism, polycystic ovary syndrome (PCOS), hypothalamic-pituitary dysfunction, and growth hormone (somatotropic hormone) deficiency.
• Pregnancy pathology. Among specific conditions associated with pregnancy, acute fatty liver of pregnancy is a predisposing factor.

Associated pathological conditions

Small intestinal bacterial overgrowth syndrome rarely occurs in isolation. Pathological changes in the bacterial landscape of the small intestine entail a number of associated pathologies affecting various body systems:

• Gastrointestinal tract: patients frequently experience diarrhea or persistent constipation. Malabsorption syndrome develops naturally, and gastritis, colitis, and peptic ulcer disease may be comorbid conditions.
• Metabolism and systemic disorders: dysbiosis can provoke both hypocholesterolemia and hypercholesterolemia. Vascular tone fluctuations (hypotension or hypertension) are noted clinically, along with an increased risk of allergic reactions and urolithiasis.
• Other localizations and risks: bacterial imbalance is associated with dental caries, joint lesions (arthritis), and inflammatory liver damage. In addition, a long-standing dysbiotic process increases the overall risk of malignancies.

Class and exam questions

What else to study on this topic

• Mechanisms of pathological bacterial translocation in liver diseases
• Malabsorption syndrome: pathophysiology in the setting of small intestinal dysbiosis
• Acute fatty liver of pregnancy and its impact on the microbiome
• The role of non-selective beta-blockers in gastroenterology
• The effect of total parenteral nutrition on the gut microbiome

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.