What is Inflammatory Diarrhea
Inflammatory diarrhea is characterized by liquid loose stools with blood or mucous discharge, resulting from colonic or intestinal inflammation that damages the mucosa and triggers an acute inflammatory response with cytokine activation. 1
Pathophysiologic Mechanism
Inflammatory diarrhea occurs through two primary pathways:
Cytotoxin-producing, noninvasive bacteria (e.g., enterohemorrhagic E. coli, C. difficile) adhere to the mucosa, activate cytokines, and stimulate the intestinal mucosa to release inflammatory mediators without direct invasion 2
Invasive organisms (e.g., Salmonella, Shigella, Campylobacter, Entamoeba histolytica) invade the intestinal mucosa to induce acute inflammatory reaction, involving cytokine activation and inflammatory mediator release 2
In inflammatory bowel disease (IBD), chronic intestinal inflammation originates from an overly aggressive mucosal immune response against luminal bacteria in genetically susceptible individuals 1
Clinical Characteristics That Distinguish Inflammatory from Other Diarrheas
Key distinguishing features include:
Stool appearance: Liquid loose stools containing visible blood or mucous, contrasting with the bulky, malodorous pale stools of malabsorption 1
Increased stool frequency with urgency and tenesmus, particularly in ulcerative colitis where mucosal inflammation starts distally in the rectum 3
Rectal bleeding occurs commonly, especially in ulcerative colitis 3
Systemic symptoms: Abdominal pain, fever, weight loss, and signs of systemic inflammation 4, 5
Diagnostic Approach
Laboratory markers:
Fecal calprotectin >100-250 μg/g indicates active intestinal inflammation with 93% sensitivity and 96% specificity for IBD 3
Elevated inflammatory markers (ESR, CRP) and anemia suggest inflammatory etiology 6
Important caveat: Fecal leukocyte examination and stool lactoferrin should NOT be used to establish the cause of acute infectious diarrhea due to poor performance, intermittent presence, and degradation during transport 1
Endoscopic evaluation:
Flexible sigmoidoscopy with biopsies is essential to confirm diagnosis and assess disease severity in suspected colonic inflammatory diarrhea 6
Colonoscopy with biopsies remains the gold standard for diagnosing ulcerative colitis and other inflammatory bowel diseases 6, 4
Common Causes
Infectious causes:
- Bacterial pathogens including C. difficile, particularly with recent antibiotic exposure 7
- Cytomegalovirus (CMV) in immunocompromised patients or those with underlying IBD 7
Inflammatory bowel disease:
- Ulcerative colitis presents with continuous inflammation limited to the colon with rectal involvement 7
- Crohn's disease shows patchy, transmural inflammation affecting any part of the gastrointestinal tract 7
Other causes:
- Ischemic colitis in older adults with vascular disease 7
- Medication-induced colitis (NSAIDs, antibiotics) 7
- Radiation colitis following pelvic radiotherapy 7
Critical Clinical Pitfalls
Always exclude infectious causes first, particularly C. difficile, before attributing symptoms to IBD flare, as infection can mimic or coexist with IBD 6
Not all colitis presents with bloody diarrhea—microscopic colitis typically presents with watery, non-bloody diarrhea despite being inflammatory in nature 7
Do not perform full colonoscopy in acute severe colitis due to perforation risk; flexible sigmoidoscopy is adequate 6
Antidiarrheal agents like loperamide are contraindicated in extremely ill patients with evidence of obstruction, colonic dilation, fever, or abdominal tenderness 8