Definition And Classification

Core Definition

• Presence of grossly visible blood in stools.
• Consequence of colonic mucosal infection by bacterial or amebic pathogens.
• Differentiated from acute watery diarrhea; denotes inflammatory enterocolitis.
• Frequent, small-volume mucoid stools.
• Accompanied by fever, abdominal pain, tenesmus (ineffectual defecation, straining, suprapubic discomfort).
• Clinically distinct from non-inflammatory bloody diarrhea (larger volume, minimal systemic toxicity).

Primary Categories

• Bacillary Dysentery: Bacterial etiology; significantly more common in pediatric populations.
• Amebic Dysentery: Parasitic etiology; insidious onset; less frequent in children.

Etiology And Pathogens

Pathophysiology

Mechanisms Of Mucosal Invasion

• Pathogens traverse intestinal epithelial barrier.
• Shigella pathogenesis: Invades M cells, utilizes cell-cell and basolateral invasion.
• Induces macrophage apoptosis, releasing interleukin-1β (IL-1β) and IL-8.
• Triggers massive polymorphonuclear leukocyte (neutrophil) transmigration.
• Disrupts tight junction proteins (claudin-1, ZO-1); dephosphorylates occludin.
• Epithelial barrier destruction creates microabscesses and frank mucosal ulcerations.

Toxin-Mediated Damage

• Enterotoxins induce secretory fluid loss early in disease course (watery diarrhea phase).
• Shiga toxin (S. dysenteriae type 1, EHEC): Inhibits cellular protein synthesis.
• Triggers endothelial damage, precipitating microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury (HUS).

Clinical Features

Acute Disease Progression

• Incubation period: Typically 1-5 days.
• Prodrome: High fever, malaise, anorexia, occasional vomiting.
• Initial phase: Watery, large-volume diarrhea.
• Dysenteric phase: Transition to frequent, small-volume stools mixed with overt blood and mucus.
• Abdominal examination: Diffuse tenderness, hyperactive or hypoactive bowel sounds.

Pathogen-Specific Manifestations

• Shigellosis: High fever >40°C, severe tenesmus, potential neurological manifestations (seizures).
• Amebiasis: Gradual, insidious onset; less prominent fever; right upper quadrant pain if liver abscess present.

Differential Diagnosis

Complications

Intestinal Complications

• Toxic Megacolon: Colonic dilation >6 cm; risk of imminent rupture; associated with Shigella, C. difficile, EHEC, E. histolytica.
• Intestinal Perforation: High mortality; free air under diaphragm on upright radiograph.
• Rectal Prolapse: Secondary to severe tenesmus and perineal muscle fatigue.
• Amebic Specific: Amebic appendicitis, colonic strictures, amebomas (granulomatous masses).

Extraintestinal Complications

• Renal: Hemolytic uremic syndrome (S. dysenteriae type 1, STEC).
• Neurological: Seizures, encephalopathy (Shigella, STEC).
• Rheumatologic: Reactive arthritis, erythema nodosum (Shigella, NTS, Campylobacter, Yersinia).
• Neuromuscular: Guillain-Barré syndrome (Campylobacter jejuni).
• Hepatic: Amebic liver abscess (E. histolytica).

Diagnostic Evaluation

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Laboratory Investigations

• Complete Blood Count (CBC): Assess for leukocytosis, bandemia (leukemoid reaction in Shigella); evaluate smear for schistocytes (HUS screen).
• Metabolic Panel: Assess baseline renal function (BUN, Creatinine) and profound dyselectrolytemia (hypokalemia, metabolic acidosis).
• Fecal Biomarkers: Elevated fecal calprotectin or lactoferrin denotes mucosal inflammation.
• Stool Microscopy: Numerous polymorphonuclear leukocytes indicate invasive bacterial colitis. Pyknotic or absent leukocytes suggest amebic dysentery (amebae destroy neutrophils).

Microbiological Assays

• Stool Culture: Isolate Salmonella, Shigella, Campylobacter (requires microaerobic conditions, 42°C), Yersinia.
• Toxin Assays: C. difficile toxin A/B EIA, Glutamate Dehydrogenase (GDH) antigen test, NAAT.
• Molecular Panels: Multiplex PCR / Nucleic Acid Amplification Tests (NAAT) highly sensitive for rapid pathogen identification.
• Parasitology: Enzyme immunoassay (EIA) or PCR for E. histolytica; direct microscopy for trophozoites/cysts (requires minimum 3 separate samples).

Endoscopy And Histology (If Refractory or IBD Suspected)

• Campylobacter: Friable mucosa, aphthoid ulcers, crypt abscesses, neutrophilic infiltrate.
• Shigella: Patchy mucosal edema, loss of vascular pattern, pseudomembranes, crypt depletion.
• E. histolytica: Deep, flask-shaped ulcer craters covered with purulent necrotic material.

Management Protocol

Resuscitation And Supportive Care

• Hydration: Primary intervention. Utilize low-osmolarity Oral Rehydration Solution (ORS) for mild-moderate dehydration.
• Intravenous Therapy: Isotonic crystalloid fluid resuscitation (20 mL/kg bolus) mandated for shock, severe dehydration, or intractable vomiting.
• Nutritional Rehabilitation: Continue breastfeeding; institute early refeeding with age-appropriate unrestricted diet to repair mucosa.
• Zinc Supplementation: Administer 5 mg/day elemental zinc for 14 days #recent. Reduces severity, duration, and prevents recurrence.
• Contraindications: Strictly avoid antimotility agents (loperamide, diphenoxylate). Prolong pathogen clearance, exacerbate tissue invasion, precipitate toxic megacolon/ileus.

Antimicrobial Pharmacotherapy

Bacillary Dysentery (Empiric and Directed)

• Do not delay therapy for culture results in toxic patients.
• Severe/Hospitalized Cases: Intravenous Ceftriaxone (50-100 mg/kg/day for 3-5 days) represents first-line empiric therapy.
• Stable/Outpatient Cases: Oral Azithromycin (10-12 mg/kg/day on day 1, followed by 5-6 mg/kg/day for 4 days) or Oral Cefixime.
• Fluoroquinolones: Ciprofloxacin (15 mg/kg/dose BID for 3 days) highly effective but restricted use in pediatrics unless alternative unavailable or pathogen sensitivity confirmed.
• Refractory Shigellosis: Adjust therapy based strictly on local resistance patterns and culture sensitivities.

Amebic Dysentery

• First-Line Tissue Agent: Metronidazole (15 mg/kg/day divided TID for 5-7 days) or Tinidazole (50 mg/kg single dose, max 2 g, for 3 days).
• Follow-up Luminal Agent: Mandatory eradication of colonized cysts post-metronidazole therapy to prevent relapse. Utilize Paromomycin (25-35 mg/kg/day divided TID for 7 days) or Iodoquinol.

Clostridioides difficile Colitis

• Immediate cessation of offending antibiotic.
• First-Line Therapy: Oral Metronidazole (30 mg/kg/day divided QID) or Oral Vancomycin (40 mg/kg/day divided QID for 10-14 days). Oral Vancomycin preferred for severe/fulminant disease.
• Recurrent/Refractory: Pulsed-tapered Oral Vancomycin, Fidaxomicin, or Fecal Microbiota Transplantation (FMT).