What could be causing an adult with no significant medical history to experience continuous diarrhea for 7 months?

Chronic Diarrhea for 7 Months: Urgent Gastroenterology Referral Required

You need an urgent gastroenterology referral within 2-4 weeks for colonoscopy with biopsies, as diarrhea lasting 7 months is classified as chronic (>30 days) and requires systematic evaluation to exclude serious organic diseases including colorectal cancer, inflammatory bowel disease, microscopic colitis, and celiac disease. 1, 2, 3

Why This Is Urgent

Seven months of continuous loose stools meets the definition of chronic diarrhea (>30 days duration), which has a fundamentally different differential diagnosis than acute diarrhea—infectious causes become unlikely, and serious organic diseases become the primary concern. 1, 4 The longer diarrhea persists, the less likely it is infectious and the more likely it represents structural, inflammatory, or malabsorptive disease requiring definitive diagnosis. 5, 6

Immediate Laboratory Testing (Complete Within 1-2 Weeks)

Order these tests now while awaiting gastroenterology:

• Complete blood count to detect anemia from iron, B12, or folate deficiency, which suggests malabsorption or chronic blood loss 2, 3, 4
• C-reactive protein or erythrocyte sedimentation rate as inflammatory markers with high specificity for organic disease like inflammatory bowel disease 2, 3, 4
• Anti-tissue transglutaminase IgA with total IgA for celiac disease screening—this is mandatory, as celiac disease is the most common small bowel enteropathy in Western populations 7, 2, 3
• Comprehensive metabolic panel to assess electrolyte disturbances from chronic diarrhea 7, 2
• Thyroid function tests to exclude hyperthyroidism as a cause 7, 2, 4
• Iron studies, vitamin B12, and folate levels to detect deficiencies 7, 2

Essential Stool Testing

• Fecal calprotectin to distinguish inflammatory from non-inflammatory causes—elevated levels indicate inflammatory bowel disease or microscopic colitis 7, 2, 3
• Stool culture and ova/parasites to exclude chronic infections like giardiasis, though less likely after 7 months 7, 2, 3
• Fecal immunochemical test (FIT) for occult blood to increase sensitivity for colorectal neoplasia 7, 2, 3

Colonoscopy Is Mandatory—Not Optional

Full colonoscopy with biopsies from both right and left colon is absolutely required, even if the mucosa appears completely normal on visual inspection. 7, 2, 3 This is critical because:

• Microscopic colitis accounts for 15% of chronic diarrhea cases in adults and has entirely normal-appearing mucosa on endoscopy but shows characteristic histologic changes only on biopsy 7, 2, 3
• Colorectal cancer has a 27% prevalence in patients with change in bowel habits, with approximately 50% of neoplasia located proximal to the splenic flexure (requiring full colonoscopy, not just sigmoidoscopy) 3
• Inflammatory bowel disease can have subtle early changes requiring histologic confirmation 2, 3

Top Priority Diagnoses to Exclude

1. Microscopic colitis (collagenous or lymphocytic colitis)—particularly common in older adults, requires histologic diagnosis, treated with budesonide 7, 2, 3

2. Inflammatory bowel disease (Crohn's disease or ulcerative colitis)—can present at any age, requires disease-specific immunosuppressive therapy 2, 3, 4

3. Celiac disease—most common small bowel enteropathy, treated with strict lifelong gluten-free diet 7, 2, 3

4. Colorectal cancer—especially if age >45 years, requires urgent exclusion 7, 3

5. Bile acid diarrhea—if colonoscopy negative, test with SeHCAT or serum 7α-hydroxy-4-cholesten-3-one, treated with cholestyramine 7, 2

Critical Pitfalls to Avoid

• Do NOT diagnose irritable bowel syndrome without completing this workup—chronic diarrhea lasting 7 months requires exclusion of organic disease first 7, 2, 3

• Do NOT skip colonic biopsies even if the mucosa looks normal—microscopic colitis is invisible to the naked eye 7, 2, 3

• Do NOT perform flexible sigmoidoscopy alone—full colonoscopy is required to evaluate the entire colon, as half of neoplasia is proximal 2, 3

• Do NOT rely on CT imaging alone—it is inadequate for detecting microscopic colitis, early inflammatory bowel disease, or subtle mucosal abnormalities 7, 2

Timeline for Action

• Blood and stool tests: Complete within 1-2 weeks 7, 3
• Gastroenterology referral: Urgent, within 2-4 weeks 7, 2, 3
• Colonoscopy: Schedule as soon as possible through gastroenterology 7, 2
• If initial workup unrevealing: Proceed to upper endoscopy and specialized testing within 4-6 weeks 7, 2, 3

Treatment Depends on Diagnosis

Treatment must be specifically tailored to the underlying cause once identified—empiric antidiarrheal therapy without diagnosis is inappropriate for chronic diarrhea of this duration. 2, 6 Specific treatments include gluten-free diet for celiac disease, budesonide for microscopic colitis, bile acid sequestrants for bile acid diarrhea, and immunosuppressive therapy for inflammatory bowel disease. 2