### Date : 2024-11-17 23:48 ### Topic : Bacterial Overgrowth Syndrome (BOS) #gastroenterology ---- ### **Bacterial Overgrowth Syndrome (Small Intestinal Bacterial Overgrowth - SIBO)** **Bacterial Overgrowth Syndrome (BOS)**, commonly referred to as **Small Intestinal Bacterial Overgrowth (SIBO)**, occurs when an **abnormal increase in the number or type of bacteria** populates the small intestine. This leads to **malabsorption**, **nutrient deficiencies**, and gastrointestinal symptoms due to fermentation and inflammation. --- ### **Pathophysiology** 1. **Normal Small Intestinal Environment**: - The small intestine normally has relatively low bacterial counts compared to the colon due to: - Acidic gastric secretions. - Intestinal motility and peristalsis. - Anatomical barriers (e.g., ileocecal valve). 2. **Pathogenesis of SIBO**: - In SIBO, the balance is disrupted, allowing excessive bacterial colonization in the small intestine. - Bacteria ferment unabsorbed carbohydrates, producing **gas** (hydrogen, methane) and **toxins**, leading to: - Mucosal injury and inflammation. - Impaired digestion and absorption of nutrients. - Increased permeability of the intestinal lining ("leaky gut"). 3. **Consequences**: - **Carbohydrate malabsorption**: Gas and bloating. - **Fat malabsorption**: Steatorrhea and fat-soluble vitamin deficiencies (A, D, E, K). - **Protein malabsorption**: Loss of lean body mass. - **Vitamin B12 deficiency**: Due to bacterial consumption. --- ### **Causes and Risk Factors** 1. **Anatomical Abnormalities**: - Small bowel diverticula. - Strictures or adhesions. - Post-surgical changes (e.g., Roux-en-Y gastric bypass). 2. **Motility Disorders**: - **Ileus**, chronic intestinal pseudo-obstruction. - Neurological conditions affecting motility (e.g., Parkinson’s disease, diabetes). 3. **Hypochlorhydria (low stomach acid)**: - Due to proton pump inhibitors (PPIs), atrophic gastritis, or post-gastrectomy. 4. **Impaired Immune Function**: - HIV/AIDS, immunosuppressive therapy. 5. **Other Factors**: - Chronic pancreatitis or exocrine pancreatic insufficiency. - Irritable bowel syndrome (IBS). - Celiac disease. --- ### **Symptoms** SIBO symptoms can range from mild to severe and overlap with other gastrointestinal disorders. #### **Gastrointestinal Symptoms**: - **Bloating**: Often severe and worsens after meals. - **Flatulence**: Due to fermentation of unabsorbed carbohydrates. - **Diarrhea**: Watery or steatorrhea. - **Abdominal pain/cramping**. - **Nausea**. #### **Systemic Symptoms**: - **Weight loss**: Due to malabsorption. - **Fatigue**: Often related to nutrient deficiencies. - **Nutritional Deficiencies**: - Vitamin B12: Leading to anemia and neuropathy. - Fat-soluble vitamins (A, D, E, K): Leading to night blindness, osteoporosis, and clotting issues. --- ### **Diagnosis** 1. **Clinical Suspicion**: - Based on symptoms and risk factors (e.g., prior surgery, motility issues). 2. **Breath Tests**: - **Lactulose or Glucose Breath Test**: - Measures hydrogen or methane gas levels produced by bacterial fermentation. - An early rise in hydrogen or methane indicates SIBO. 3. **Small Intestinal Aspiration and Culture** (Gold Standard): - Direct sampling of small intestinal fluid via endoscopy and bacterial count >10⁵ colony-forming units/mL confirms SIBO. 4. **Blood Tests**: - Look for secondary effects like anemia (iron or B12 deficiency) or hypoalbuminemia. 5. **Imaging**: - CT or MRI to assess for anatomical abnormalities or conditions predisposing to SIBO. --- ### **Treatment** #### **1. Address Underlying Causes** - Treat motility disorders, anatomical issues, or conditions like celiac disease. #### **2. Dietary Modifications** - **Low FODMAP Diet**: - Reduces fermentable carbohydrates that fuel bacterial overgrowth. - **Elemental Diet**: - Nutritionally complete liquid diet to starve bacteria while providing nutrients. #### **3. Antibiotic Therapy** - Short courses of antibiotics reduce bacterial load: - **Rifaximin**: Non-absorbable antibiotic, effective for hydrogen-producing SIBO. - **Metronidazole** or **Ciprofloxacin**: Alternatives for mixed infections. - **Neomycin**: Effective for methane-predominant SIBO (combined with rifaximin). #### **4. Prokinetics** - Improve small intestinal motility: - **Erythromycin (low-dose)**. - **Metoclopramide** or **prucalopride**. #### **5. Nutritional Supplementation** - Replace deficiencies: - **Vitamin B12**: IM injections for severe deficiency. - **Fat-soluble vitamins (A, D, E, K)**. - **Iron, calcium**, or **zinc** as needed. #### **6. Probiotics** - May restore balance to gut flora, though evidence for effectiveness in SIBO is limited. --- ### **Prognosis** - With proper treatment, symptoms often improve. - Recurrence is common unless underlying causes are corrected. - Chronic or untreated SIBO can lead to long-term complications, including **nutritional deficiencies**, **osteoporosis**, and **intestinal damage**. --- ### **Key Points** 1. **Bacterial Overgrowth Syndrome (SIBO)** results from excessive bacterial colonization in the small intestine. 2. Symptoms include **bloating, diarrhea, malnutrition**, and **nutrient deficiencies**. 3. Diagnosis involves **breath tests** or direct small bowel cultures. 4. Treatment focuses on **antibiotics, dietary changes,** and managing underlying conditions. ### Reference: - ### Connected Documents: -