Investigation of Choice for Chronic Diarrhea in a 46-Year-Old Male
For a 46-year-old man with chronic diarrhea, colonoscopy with ileoscopy and biopsies is the investigation of choice. 1
Age-Stratified Approach
At 46 years old, this patient falls into the critical age category where full colonic imaging is mandatory due to increased risk of colorectal neoplasia. The British Society of Gastroenterology guidelines explicitly state that patients over 45 years with chronic diarrhea require colonoscopy (with ileoscopy) as the preferred investigation 1. This differs from younger patients (<45 years) where flexible sigmoidoscopy may suffice.
Why Colonoscopy is the Investigation of Choice
The evidence strongly supports colonoscopy for several reasons:
- Diagnostic yield of up to 30% in patients over 45 with chronic diarrhea 1
- Superior sensitivity compared to barium enema 1
- Allows tissue sampling for histological examination, which is essential 1
- Detects neoplasia: approximately 27% of patients with altered bowel habits have colonic neoplasms, with 50% located proximal to the splenic flexure (requiring full colonoscopy, not just sigmoidoscopy) 1
- Identifies inflammatory bowel disease and microscopic colitis: diagnostic yield of 7-31% for these conditions 1
Critical Biopsy Protocol
Random biopsies from the right and left colon (not rectum) are essential even if the mucosa appears normal 2. This is crucial because:
- Microscopic colitis affects 13% of patients with chronic diarrhea 3
- Rectosigmoid biopsies alone have a 34-43% false negative rate for microscopic colitis 1
- Samples from ascending and transverse colon maximize diagnostic accuracy 1
Routine Ileoscopy Adds Value
Ileoscopy should be performed routinely during colonoscopy:
- 18% diagnostic yield in non-HIV patients with diarrhea 1
- 36% of patients with normal colonoscopy but diarrhea have terminal ileal disease 1
- Particularly important when inflammatory bowel disease is suspected (diagnostic yield approaches 40%) 1
Initial Screening Tests Before Colonoscopy
While colonoscopy is the investigation of choice, initial blood and stool screening should be performed first 1, 2:
Blood tests:
- Full blood count, ESR, electrolytes, liver function tests
- Iron studies, vitamin B12, folate
- Thyroid function tests
- Tissue transglutaminase IgA antibodies (with total IgA) for celiac disease 2
Stool tests:
- Faecal calprotectin to assess for inflammation 2
These screening tests help direct whether the focus should be on colonic, small bowel, or pancreatic disease 1.
When to Consider Additional Investigations
If colonoscopy with biopsies is normal and symptoms persist, consider:
- Upper endoscopy with distal duodenal biopsies if malabsorption is suspected (even with negative celiac serology) 1
- SeHCAT testing or serum 7α-hydroxy-4-cholesten-3-one for bile acid diarrhea 2
- Faecal elastase if pancreatic insufficiency is suspected 2
- MR enterography or video capsule endoscopy for small bowel evaluation (not barium studies, which have poor sensitivity) 2
Common Pitfall to Avoid
Do not perform flexible sigmoidoscopy alone in this age group. The guidelines are explicit that patients over 45 require full colonoscopy because approximately 50% of neoplasms are proximal to the splenic flexure and would be missed by sigmoidoscopy 1. The increased risk of colorectal cancer in males over 45 makes this age-stratified approach critical 1.